Friday 22 December 2017

How can a 0.5 molal solution be less concentrated than a 0.5 molar solution?

The answer lies in the units being used.


"Molar" refers to molarity, a unit of measurement that describes how many moles of a solute are in a given volume of solvent (measured in liters). By comparison, molality evaluates moles of substance per kilogram of solvent. 


Say, for example, we had 1 mole of a solute, and we were dissolving it in 1 liter of solvent, which weighed 2kg. The molarity would be 1/1, or 1,...

The answer lies in the units being used.


"Molar" refers to molarity, a unit of measurement that describes how many moles of a solute are in a given volume of solvent (measured in liters). By comparison, molality evaluates moles of substance per kilogram of solvent. 


Say, for example, we had 1 mole of a solute, and we were dissolving it in 1 liter of solvent, which weighed 2kg. The molarity would be 1/1, or 1, and the molality would be 1/2, or 0.5.


So, as long as the volume and the mass of the solvent are different values, we will get different molarity and molality measurements for the same solution.


Back to the original question; how can the same numbers result in solutions that are less concentrated in molality than molarity? The answer requires a little wordplay. 


In both cases, we have half a mole of solute. That aspect is pretty straightforward. The concentration is another way of talking about density; how many particles of solute i find in a given volume of solvent. In the less concentrated solution, I should find fewer particles of solute, meaning they are spread out more. Therefore, this tells us that the 0.5 molal solution must have a greater volume than the 0.5 molar solution. In fact, if we were to evaluate the 0.5 molal solution in terms of molarity, it would have a lower value, and that would confirm our expectation.

In one sentence, characterize Dally's relationship with Johnny.

Dally and Johnny share a unique friendship, characterized by similar admiration, mutual respect, and indirect compassion for one another.


Dally and Johnny both come from broken homes and are significant members of the Greaser gang. Johnny views Dally as a hero for his courage and loyal attitude. Dally cares deeply about his good friend Johnny and goes out of his way several times throughout the novel to help Johnny out. Since Dally has a "tough"...


Dally and Johnny share a unique friendship, characterized by similar admiration, mutual respect, and indirect compassion for one another.



Dally and Johnny both come from broken homes and are significant members of the Greaser gang. Johnny views Dally as a hero for his courage and loyal attitude. Dally cares deeply about his good friend Johnny and goes out of his way several times throughout the novel to help Johnny out. Since Dally has a "tough" image to uphold, he seldom displays his compassion for his friend. Dally also views Johnny as his younger brother and even risks his life and freedom for Johnny. There are several scenes throughout the novel that depict Johnny and Dally's true feelings for each other. When the boys go to Dairy Queen to eat, Dally flips out because he doesn't want Johnny to go to jail. Dally displays his love for Johnny by explaining to Johnny how he doesn't want Johnny to end up callous and emotionless like he did. Another scene that depicts their true feelings for one another is when Johnny is lying on his death bed, and he lets Dally know that fighting is useless. Johnny was giving potentially life-saving news to his good friend, but unfortunately, Dally lost his mind after Johnny died.

What is the life stage when a star expands and cools?

During the main sequence of its life cycle, the same stage that our Sun is currently in, a star obtains its energy from nuclear fusion of hydrogen to helium. This nuclear reaction goes on for a very long time, till all the hydrogen in the core of the star is used up. When that happens, the core no longer has a nuclear reaction going on and in absence of the reactions, the core begins to...

During the main sequence of its life cycle, the same stage that our Sun is currently in, a star obtains its energy from nuclear fusion of hydrogen to helium. This nuclear reaction goes on for a very long time, till all the hydrogen in the core of the star is used up. When that happens, the core no longer has a nuclear reaction going on and in absence of the reactions, the core begins to contract. This causes an increase in the core's temperature and a new nuclear fusion reaction starts, in which helium fuses to carbon. This new reaction causes the outer envelope to expand and the star becomes larger in size. This also causes the star to cool down and to appear red. This phase of the star's life cycle, when it has expanded to a very large size and has cooled down, is known as the red giant phase and the star is said to have become a red giant.


The next stage of star's life cycle depends on its mass, with one path leading to white dwarf stage and another leading to neutron star and black hole stages.

How effective was the New Deal legislation in bringing the US out of the Depression?

Most historians would say that the New Deal programs were at least somewhat effective in getting the United States out of the Great Depression.  They would say that the New Deal began to get the country out of the Depression, but they would also say that the programs were not enough to get the country completely back on track.  The United States only really got back to prosperity when it started to prepare for World War II.

Almost all historians (outside of some conservatives) believe that the New Deal really did help the economy.  The numbers suggest that this is true.  As you can see in the link below, the US economy bottomed out in 1932 before President Franklin Roosevelt was elected.  After he was elected and started to implement the New Deal, the economy clearly improved, though it did suffer another downturn in 1937.  This suggests that the New Deal actually caused the economy to improve.  (Conservative economic historians believe that the recovery would have been faster and longer-lasting if the government had not implemented the New Deal.) 


However, it is also clear that the economy remained very weak for years after the New Deal began.  By 1939, the US’s GDP was still no higher than it had been before the Depression began.  This means that, even after the New Deal had six years to work, it had still not really gotten the economy back on track.  Instead, the economy did not manage to take off until 1939, when the US started to manufacture more military materiel as it prepared for World War II.  This is why historians generally say that the New Deal managed to help stop the Depression, but that it did not actually end that economic crisis. 

Thursday 21 December 2017

What are mushrooms/psilocybin? |


History of Use

Hallucinogenic mushrooms containing psilocybin are thought to have existed as long or longer than the human race. Historically, artwork such as pictures, statues, and carvings depicting the mushrooms have been seen near tribal settlements. In Central and South America, psilocybin-containing mushrooms were commonly used in religious ceremonies until Spanish settlers spread Catholicism and banned their use. Mushrooms are sacred to indigenous peoples and are considered entheogens, psychoactive substances that guide their religious path through the spirit world.




In the early twentieth century ethnobotanists Richard Evans Schultes and Blas Pablo Reko traveled to Mexico and sought out these mushrooms. Schultes published a report of his findings in 1939. After hearing of this work, ethnomycologists Roger Heim and R. Gordon Wasson and pediatrician Valentina Wasson traveled to Central America to investigate the use and effects of the mushrooms. In 1957 the Wassons published the article “Seeking the Magic Mushroom” in Life magazine.


Mushrooms symbolized hippie counterculture in the 1960s and 1970s and were commonly used in the United States and Great Britain. The mushrooms led to the discovery of LSD, a synthetic hallucinogen.


It is difficult to determine the level of use of psilocybin-containing mushrooms because most studies of drug use neglect to include this drug. The Monitoring the Future survey published in 2008 reported that 7.8 percent of high school seniors had used hallucinogens other than LSD. This group of drugs includes peyote and psilocybin. Use in the previous year by participants was reported as 5 percent.




Effects and Potential Risks

Psilocybin and its active form, psilocin, are not inactivated by heating or freezing. To mask its bitter flavor, the mushroom is brewed into tea or cooked with other foods. Digestion and absorption of the psilocybin take about twenty minutes, and the effects last from four to six hours.


Psilocybin can produce relaxation or weakness of the muscles, lack of coordination, excessive pupil dilation, nausea, vomiting, and drowsiness. Mushroom abusers are at risk of poisoning if poisonous mushrooms are accidentally ingested with psilocybin mushrooms.


The psychological effects of psilocybin use include hallucinations, an altered perception of the passage of time, and confusion between fantasy and reality. Panic and psychosis also may occur, especially with high doses. Persistent use comes with flashbacks, risk of psychiatric disease, memory impairment, and tolerance.




Bibliography


Laing, Richard R., ed. Hallucinogens: A Forensic Drug Handbook. San Francisco: Elsevier, 2003. Print.



“Hallucinogens: LSD, Peyote, Psilocybin, and PCP.” National Institute on Drug Abuse. National Inst. of Health, 2009. Web. 10 Mar. 2012.



Health Day. "MRIs Showed Brain Activity That Mirrored What's Seen in a Dream-Like State." Patient Education Resource Center. EBSCO, 3 July 2014. Web. 27 Oct. 2015.



Pollan, Michael. "The Trip Treatment." New Yorker. Condé Nast, 9 Feb. 2015. Web. 27 Oct. 2015.



“Psilocybin Mushrooms.” Erowid.org. Erowid, n.d. Web. 26 Mar. 2012.

Which aspects of Romantic literature can be perceived in William Blake's poem "London?"

Romanticism is characterized by the glorification of nature, the celebration of the individual, and the emphasis on imagination and emotion. So, with "London" we don't see those themes overtly. But the poem is a scathing critique of the city, tradition, and institutions. This suggests a preference for nature, individuality, and freedom. 


Blake condemns the culture of the city. Since London is the capital, he is condemning English culture in general. Blake believed that people were...

Romanticism is characterized by the glorification of nature, the celebration of the individual, and the emphasis on imagination and emotion. So, with "London" we don't see those themes overtly. But the poem is a scathing critique of the city, tradition, and institutions. This suggests a preference for nature, individuality, and freedom. 


Blake condemns the culture of the city. Since London is the capital, he is condemning English culture in general. Blake believed that people were brainwashed ("mind-forg'd manacles) into accepting this (then) modern, urban way of life. Blake sees the city, government, and the church as oppressive institutions. The Soldier is sent off to fight and possibly die. Blake even critiques marriage when he refers to the "Marriage hearse." People accept that marriage is a necessary path in life and this potentially leads to loveless unions. As a result, some are driven to prostitutes. He is saying that a tradition (marriage in this case) can imprison people and suppress their emotions. 


Blake's critique of tradition and institutions is part of the Romantic themes that we see in other of his works. His critique of tradition and the city suggests alternatives such as individuality, breaking with tradition, and the notion that nature provides an alternative to the urban decay he sees in city life. 

Wednesday 20 December 2017

What is kidney infection? |


Definition

Kidney infection occurs when there is a bacterial
infection in one or both kidneys. The kidneys remove waste
(in the form of urine) from the body. They also balance the water and electrolyte
content in the blood by filtering salt and water.










Causes

Kidney infection may be caused by, most commonly, a bladder infection that was not treated or inadequately treated;
conditions that slow the flow of urine from the bladder, such as an enlarged
prostate or kidney stones; having a cystoscopy
done to examine the bladder; surgery of the urinary tract; use of a catheter to drain urine from the bladder; and, rarely, bacteria from
another part of the body that has entered the kidneys.




Risk Factors

The factors that increase the chance of developing kidney infection include
sexual activity; pregnancy; diabetes; birth disorder of the urinary tract,
including vesicoureteral reflux; blockage of the urinary tract, including tumors,
an enlarged prostate gland, kidney stones, or a catheter or stent placed in the
urinary tract; polycystic kidneys; sickle cell anemia; previous kidney
transplant; and a weakened immune system. Also, girls and women are at greater
risk for kidney infection.




Symptoms

Symptoms include pain in the abdomen, lower back,side, or groin; frequent urination; urgent urination that produces only a small amount of urine; sensation of a full bladder, even after urination; burning pain with urination; fever and chills; nausea and vomiting; pus and blood in the urine; and loss of appetite.




Screening and Diagnosis

A doctor will ask about symptoms and medical history and will perform a physical exam. Kidney infection is diagnosed with urine tests. The urine is examined for bacteria, white blood cells, blood, and other abnormal elements.


If the infection does not go away after treatment or if the person has had
several kidney infections, other tests might be ordered to see if there are
problems with the kidney, ureters, and bladder. These tests include a kidney
ultrasound (a test that uses sound waves to examine the kidney); an abdominal
computed
tomography (CT) scan (a detailed X-ray picture that
identifies abnormalities of fine tissue structure); and a voiding
cystourethrography (an X ray of the urinary bladder and urethra made after
injection with a contrast medium).




Treatment and Therapy

Kidney infections are treated with antibiotics. If the infection is not
treated correctly or is left untreated, the condition can lead to septicemia (a
blood infection that has spread throughout the body), chronic infection, scarring
of the kidney, or permanent kidney damage. In some cases, the infected person may
need to be hospitalized and may need to receive antibiotics intravenously.




Prevention and Outcomes

Because kidney infection is often a complication of a bladder infection, the chance of getting a bladder infection can be lessened by drinking increased amounts of fluids (about eight to ten 8-ounce glasses per day); this includes drinking cranberry juice, which may help prevent bladder infection too. Other preventive measures are to practice good hygiene, to urinate when the need arises, and to take showers rather than baths. Women should wipe from the front to the back after using the toilet, should urinate before and after having sex, and should avoid douches and genital deodorant sprays.




Bibliography


Brenner, Barry M., ed. Brenner and Rector’s The Kidney. 8th ed. Philadelphia: Saunders/Elsevier, 2008.



Greenberg, Arthur, et al., eds. Primer on Kidney Diseases. 4th ed. Philadelphia: Saunders/Elsevier, 2005.



Kiel, Raphael, et al. “Does Cranberry Juice Prevent or Treat Urinary Tract Infection?” Journal of Family Practice 52, no. 2 (February, 2003): 154-155.



O’Callaghan, C. A., and Barry M. Brenner. The Kidney at a Glance. Malden, Mass.: Blackwell Science, 2000.



Parker, James N., and Philip M. Parker, eds. The 2002 Official Patient’s Sourcebook on Pyelonephritis. San Diego, Calif.: Icon Health, 2002.



Walsh, Patrick C., et al., eds. Campbell-Walsh Urology. 4 vols. 9th ed. Philadelphia: Saunders/Elsevier, 2007.

What is ophthalmology? |


Science and Profession

Among the sense organs and functions in the body, probably the most complex are the eye and the process of vision that it supports. Ophthalmologists study both the anatomy and the physiology of the eye in order to understand and treat common and rare eye infections and disorders.



The principal anatomical element of vision is the eyeball, or eye globe, located in the right and left orbital openings of the skull. It is embedded in a complex system of tissues surrounded by ocular muscles that control its movement. Adjacent to the eye and also within the bony orbit is the lacrimal gland, which is responsible for keeping the eye moist. Only the front third of the globe is exposed. This exposed area is made up of the central transparent portion, the cornea, and a surrounding white portion, which is only part of the sclera, the main component mass of the globe itself. The sclera is a very dense collagenous (protein-rich) structure which has two large openings (the anterior and posterior scleral foramina) and a number of smaller apertures that allow for the passage of nerves and blood vessels into the eye. It is through the posterior scleral foramen that three main components sustaining the eye’s functions pass: the optic nerve, the central retinal vein, and the central retinal artery.


The eye has three main layers, within which are further specialized divisions. The outer layer consists essentially of the transparent cornea and opaque sclera. The middle layer, called the uvea, is made up of the choroid, which is the outer coating of the layer; the ciliary body, which contains key eye muscles that affect the degree of curvature in the lens; and the iris, which, with the lens located immediately behind it, separates the anterior from the posterior chambers of the eye. This iris itself has two layers, the stroma and the epithelium. The latter is immediately recognizable to the layperson, since its cells are markedly pigmented, giving to each individual a characteristic eye color.


It is the opening in the iris, called the pupil, that allows the passage of light into the inner layer of the eye, which contains the key sensory portion of the organ, the retina. Before light reaches the inner layer and the retina, it passes through the lens of the eye, located immediately behind the iris (which it supports), and through the largest area of open space within the eye, the vitreous cavity. This posterior cavity, like the smaller forward cavity of the eye, is filled with a transparent hydrogel called aqueous humor, made up mainly of water (about 95 percent of its total mass) in a collagenous framework within which the main component is hyaluronic acid. The aqueous humor is very similar to plasma but lacks its protein concentration. The pupil of the eye serves a purpose similar to the diaphragm (or f-stop) on a camera; it opens wider (dilates) or closes (contracts) according to the intensity of light striking the eye. (This reaction explains why, after a few minutes in an apparently totally dark room, the eye adjusts at least in part to the lower intensity of light.) For purposes of examining the internal structures of the eye, ophthalmologists sometimes place special drops in the eye to cause the pupil to dilate.


The lens of the eye, which is held in place behind the pupil by zonular fibers, consists of onionlike lens fibers. These are the product of epithelial cells that “migrate” from their place of origin in a germinative zone next to the edges of the lens to the anterior portion of the concentric structure of the lens. The central or internal layers of lens fibers, called the embryonic nucleus, represent the earliest cell specialization processes before birth. By contrast, the anterior and posterior lens fibers are constantly renewed at the surface.


As light passes through the transparent lens fibers, the phenomenon of refraction results, in the simplest possible explanation, both from the concentric shape of the lens itself and from a differential in the index of refraction occurring in the “younger” outside layers of lens fibers and that of the “older” central layers; the latter have a greater index of refraction than the former. Another phenomenon that increases the refractive power of the lens occurs when the zonular fibers that hold it in place relax under the influence of the ciliary muscle, making the lens more spherical in shape. The resultant increase in refractive power is called accommodation.


It is the retina, located in the last layer of the eye, that receives the light images passing through the lens and transmits them to the brain via the optic nerve. Physiologists consider the nerve-related function of the retina to be comparable in many details with all other sensory phenomena in the body, including touch and smell. The retina itself consists of a very thin outer layer, called the retinal pigment epithelium, and an inner layer, the sensory retina. On the surface of the retina, one finds a layer of photoreceptor cells. Once affected by the absorption of light rays reaching them from the lens, these cells form synapses with an intermediate layer of modulator cells. A synaptic relationship may be defined as an excitatory functional contact between two nerve cells, causing either a chemical or an electrical response. The modulator cells—referred to as neurons when their function is to receive synaptic transmissions from receptor cells—in turn pass the “message” of light to ganglion cells forming the innermost cellular layer of the retina. These cells transmit electrical discharges through the optic nerve to the brain, where they are registered as images.




Diagnostic and Treatment Techniques

Ophthalmologists must deal with a wide variety of problems affecting the eyes, ranging from injuries to the diagnosis of vision problems that can be corrected with eyeglasses or contact lenses. Perhaps the most important area of applied ophthalmology, however, involves treating the diseases that may occur in several areas of the eye.


An entire category of diseases can appear in the conjunctiva, the thin mucous membrane that lines the inner portion of the eyelid and covers the exterior of the sclera. Conjunctivitis refers to inflammatory conditions that may attack this membrane. Some conditions cause mere irritation, while others may lead to serious infections. In acute catarrhal, or mucopurulent, conjunctivitis, the conjunctival blood vessels become congested with mucus and then with pus, which accumulates on the margins of the eyelids. If untreated, this form of contagious, easily transmitted infection begins to affect the cornea, by causing prismatic distortions and eventually abrasions that may infect the cornea itself. A more serious form of conjunctivitis is referred to as purulent conjunctivitis; it is sometimes associated with complications of the sexually transmitted disease gonorrhea.


Inflammation of the cornea, or keratitis, usually comes from the passage of virulent organisms from the conjunctival sac, which, although exposed to the external environment, may not itself react to the presence of bacteria. There are many different types of keratitis. Individuals may be vulnerable to infections in the cornea as a result of abrasions (one of the main reasons that all ophthalmologists recommend against rubbing the eye to remove irritating particles) or because of abnormal conditions affecting the surface of the cornea. Among the latter, ophthalmologists list excessive dryness in the eye and the side effects of malnutrition leading to a condition called keratomalacia, which is common in underdeveloped countries.


Bacteria such as pneumococci (the primary contributor to pneumonia in the lungs) may cause infections that result in corneal ulceration, the most common form of keratitis. In such cases, the area affected by the ulceration may increase considerably as epithelial tissue in the cornea attaches itself to the ulcer. Corneal ulcers may be removed by surgery, although the effect of remaining scar tissue may reduce the level of vision. The prospect of success in corneal transplantion has not eliminated the need for ulcer removal surgery, since transplants depend on the availability of “fresh” cornea donors.


Another form of corneal infection, herpes zoster (a form of skin rash also called shingles), is caused by the virus that causes chickenpox; it is common among aged patients whose cellular immunity systems suffer from decreased efficiency. In herpes zoster ophthalmicus, an infection that begins in the eye spreads via the nasociliary branch of the ophthalmic nerves and appears as red blotches on the surface of the skin (usually near the eye orbits on the side of the infection only). Zoster attacks are accompanied by rather severe pain. Ophthalmologists use several key drugs to treat this condition, including Distalgesic, Fortral, or Pethidine. Resultant depression in the patient may be relieved by prescribing amitriptyline.



Inflammation and possible infection of other regions of the eye also occur. Some zones, such as the sclera, tend to be more resistant to invasion because of the density of their fibrous tissues. Superficial inflammation of the sclera, called episcleritis, may be transitory but recurrent. Ophthalmologists will prescribe the anti-inflammatory drug Tandearil in the form of drops. More serious but much less common is the condition called scleritis, which extends much deeper into the tissue of the sclera and may affect the cornea and the uveal tract in the middle layer of the eye. Treatment of scleritis involves the use of steroid therapy, such as the corticosteroid drug prednisolone, often supplemented with Tandearil.


Uveitis is a term that applies to inflammations that occur in the uveal tract. The name suggests that such complications are not limited to one or another of the parts of the uveal zone (the iris or the ciliary body): All are affected and must be treated simultaneously; some natural treatments for uveitis have been suggested.


The most common vision problem is myopia (nearsightedness). While most people still choose to correct nearsightedness with contact lenses or glasses, laser techniques such as photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) have shown some promise in treating myopia. Early enthusiasm for radial keratotomy has waned because of erratic results.


The most widely known eye disorders are probably glaucoma and cataracts. Glaucoma occurs when pressure caused by an excessive amount of aqueous humor increases inside the eyeball, specifically in the area of the retina. Impairment of vision may be slight, occurring at first in the peripheral area of sight. Further deterioration, however, may lead to blindness in the eye. Regular treatment with drugs that reduce the production of aqueous humor is necessary in patients suffering from chronic glaucoma. Acute glaucoma, which is very sudden, represents only about one-tenth of recorded cases. It must be treated within less than a week to avert permanent blindness.



Cataracts occur when there is a loss of full transparency in the lens of the eye. Cataracts occurring among children are congenital or hereditary in origin. Cataract-like damage to the lens of the eye may also result from exposure to the sun’s rays (which is especially dangerous when one views the sun without protection during eclipses), extreme heat, x-rays, or nuclear radiation. Most characteristically, however, cataracts (from slight to advanced stages) are associated with the aging process. Formerly, cataract surgery was difficult and the recovery period slow, so patients were advised to wait as long as possible to have cataracts removed. Improvements in surgical techniques and materials mean that patients no longer need to wait until their vision is severely impaired to have this surgery. Most cataract extractions are combined with implantation of an intraocular lens, so that patients do not need to wear specially prescribed contact lenses or thick glasses following surgery.


Ophthalmologists make use of laser surgery for an increasing number of eye disorders. Lasers are used to treat eye problems caused by diabetes and hypertension, to treat or prevent some types of glaucoma, and to treat other, rarer eye conditions. Macular degeneration, an important cause of decreased central vision, may be arrested by laser therapy, but the technique does not repair existing damage.


Microsurgical techniques have further revolutionized eye care and have led to more effective management of conditions (such as retinal detachment) that formerly caused blindness.




Perspective and Prospects

Knowledge of the anatomy and physiology of the eye evolved gradually through history and then spectacularly in the latter half of the twentieth century. The most extraordinary advances in the later period were made in the field of eye surgery. For an understanding of how vision itself worked, it took centuries for surprisingly unscientific views to cede to the first modern theories and then, with the advance of anatomical dissection, the practical possibility of examining both normal and abnormal conditions of the organ in the laboratory.


An early but not widespread theory of how the eye sees, held into the Middle Ages, depended on what now seems to be the fantastic conception of eidola, or “skins.” Those who believed this theory held (in part correctly) that something must be leaving the objects that one perceives through the eyes. This “something” was thought to be a skinlike picture that, once detached from the object in question, actually entered the eye (after an unexplainable physical contraction) through the pupil, the aperture in the eye that is visible in many different animals. Another widespread theory was a prescientific version not of light rays but of “visual rays” that were thought to leave the interior of the eye, returning to record the colors and shapes of objects encountered.


Historians generally agree that the tenth-century Arab scientist ibn al-Haytham, known in the West as Alhazen, was the first to suggest that rays of light entered the eye to stimulate what he called the “sensorium.” Although Alhazen’s theory predated a scientific explanation of the nature of light itself, he based his views on the phenomenon of the lingering image on the eye’s “sensorium” of strong light, particularly that of the sun, even after the eyelids closed out the object emitting light. He even proposed a basic theory of refraction of light inside the eye. According to his theory, the sensorium recorded images according to an exact formula that reconstituted both the “shape” and the “order” in which rays are received by the eye, depending on the angle at which they strike the spherical surface of the cornea. Alhazen even warned that although the eye’s sensorium always duplicated this formula exactly, the observer (actually, the observer’s brain) could be “tricked” by the reproduction of certain ray patterns that might resemble something that was not “real”—the optical illusion.


Alhazen’s views would be examined and extended during the late sixteenth and mid-seventeenth centuries in the West by the scientific pioneers of optics, specifically the Italian Francesco Maurolico (died 1575) and the famous German astronomer Johannes Kepler (1571–1630). Kepler’s best-known work complemented that of his Italian contemporary Galileo Galilei (1564–1642), marking a breakthrough in the science of optics and the use of lenses to make telescopes in order to explore the skies. Only in later generations, however, did the ophthalmological relevance of some of his findings concerning the measurement of light reflected off the objects “seen” by a lens become clear.


As specialized interest in the eye progressed along with the constant advance of science in the eighteenth and nineteenth centuries, exact observation of the internal features of the organ of vision hinged on both the historical progress of anatomical dissection and the development of instruments to look into the living eye. One of the principal figures who contributed to the latter field was the Swedish ophthalmologist Allvar Gullstrand (1862–1930). Gullstrand received the Nobel Prize in Physiology or Medicine in 1911 for his application of physical mathematics to the study of refraction of light in the eye. He gained additional worldwide attention for his research on astigmatism (the failure of rays to be focused by the lens accurately on a single central point) and for devising the so-called slit lamp for viewing the interior of the eye through the use of an intense beam of light.


In the area of eye surgery, a major landmark was achieved in the 1960s when the Spanish ophthalmologist Ramón Castroviejo began to develop a method for surgical transplant of fully transparent corneas from deceased donors to replace damaged corneas in eye patients.




Bibliography


Buettner, Helmut, ed. Mayo Clinic on Vision and Eye Health: Practical Answers on Glaucoma, Cataracts, Macular Degeneration, and Other Conditions. Rochester: Mayo Foundation for Medical Education and Research, 2002. Print.



Kaufman, Paul L., and Albert Alm. Adler’s Physiology of the Eye: Clinical Application. 10th ed. St. Louis: Mosby, 2003. Print.



"Healthy Eyes, Healthy Body." Museum of Vision. Foundation of the American Academy of Opthalmology, 2011. Web. 17 Feb. 2015.



Newell, Frank W. Ophthalmology. 8th ed. St. Louis: Mosby, 1996. Print.



Palay, David A., and Jay H. Krachmer, eds. Primary Care Ophthalmology. 2d ed. Philadelphia: Mosby/Elsevier, 2006. Print.



Remington, Lee Ann. Clinical Anatomy of the Visual System. New York: Butterworth-Heinemann/Elsevier, 2012. Print.



Riordan-Eva, Paul, and John P. Whitcher. Vaughan and Asbury’s General Ophthalmology. 17th ed. New York: Lange Medical, 2007. Print.



Ronchi, Vasco. Optics: The Science of Vision. Trans. and rev. by Edward Rosen. Rev. ed. New York: Dover, 1991. Print.



Spalton, David J., Roger A. Hitchings, and Paul A. Hunter, eds. Atlas of Clinical Ophthalmology. 3d ed. Oxford: Mosby, 2013. Print.



Sutton, Amy L., ed. Eye Care Sourcebook: Basic Consumer Health Information About Eye Care and Eye Disorders. 3d ed. Detroit: Omnigraphics, 2008. Print.



Yanoff, Myron, and Jay S. Duker, eds. Ophthalmology. 3d ed. St. Louis: Mosby, 2009. Print.

What is conception? |


Process and Effects

The process of conception begins with the act of intercourse. When the male’s penis is inserted into the female’s vagina, the stimulation of the penis by movement within the vagina triggers a reflex resulting in the ejaculation of sperm. During ejaculation, involuntary muscles in many of the male reproductive organs contract, causing semen, a mixture of sperm and fluid, to move from its sites of storage out through the urethra within the penis.



The average volume of semen in a typical human ejaculation is only 3.5 milliliters, but this small volume normally contains two hundred million to four hundred million sperm. Other constituents of semen include prostaglandins, which cause contractions of involuntary muscles in both the male and the female; the sugar fructose, which provides energy to the sperm; chemicals that adjust the activity of the semen; and a number of enzymes and other chemicals.


In a typical act of intercourse, the semen is deposited high up in the woman’s vagina. Within a minute after ejaculation, the semen begins to coagulate, or form a clot, because of the activation of chemicals within the semen. Sperm are not able to leave the vagina until the semen becomes liquid again, which occurs spontaneously fifteen to twenty minutes after ejaculation.


Once the semen liquefies, sperm begin moving through the female system. The path to the ovum (if one is present) lies through the cervix, then through the hollow cavity of the uterus, and up through the oviduct, where fertilization normally occurs. The sperm are propelled through the fluid within these organs by the swimming movements of their tails called flagella, as well as by female organ contractions that are stimulated by the act of intercourse and by prostaglandins contained in the semen. The contractions allow sperm to reach the oviduct within five minutes after leaving the vagina, a rate of movement that far exceeds their own swimming abilities.


Although some sperm can reach the oviduct quite rapidly, others never enter the oviduct at all. Of the two hundred million to four hundred million sperm deposited in the vagina, it is estimated that only one hundred to one thousand enter the oviducts. Some of the other millions of sperm may be defective, lacking the proper swimming ability. Other apparently normal sperm may become lost within the female’s organs, possibly trapped in clefts between cells in the organ linings. The damaged and lost sperm will eventually be destroyed by white blood cells produced by the female.


Sperm movement through the female system is enhanced around the time of ovulation. For example, at the time of ovulation, the hormones associated with ovulation cause changes in the cervical mucus that aid sperm transport. The mucus at that time is extremely liquid and contains fibers that align themselves into channels, which are thought to be used by the sperm to ease their passage through the cervix. The hormones present at the time of ovulation also increase the contractions produced by the uterus and oviduct, and thus sperm transport through the structures is enhanced as well.


During transport through the female system, sperm undergo a number of important chemical changes, collectively called capacitation, that enable them to fertilize the ovum successfully. Freshly ejaculated sperm are not capable of penetrating the layers surrounding the ovum, a fact that was uncovered when scientists first began to experiment with in vitro fertilization (the joining of sperm and ovum outside the body). Capacitation apparently occurs during transport of the sperm through the uterus and possibly the oviduct, and it is presumably triggered by some secretion of the female reproductive system. With in vitro fertilization, capacitation is achieved by adding female blood serum to the dish that contains the sperm and ovum. Capacitation is not instantaneous; it has been estimated that this process requires an hour or more in humans. Even though the first sperm may arrive in the vicinity of the ovum within twenty minutes after ejaculation, fertilization cannot take place
until capacitation is completed. In 2003, scientists discovered that sperm has a type of chemical sensor that causes the sperm to swim vigorously toward concentrations of a chemical attractant. While researchers long have known that chemical signals are an important component of conception, the 2003 findings were the first to demonstrate that sperm will respond in a predictable and controllable way, a fact promising for future contraception and fertility research.


The site where ovum and sperm typically come together is within the oviduct. At the time of ovulation, an ovum is released from the surface of the ovary and drawn into the upper end of the oviduct. Once within the oviduct, the ovum is propelled by contractions of the oviduct and possibly by wavelike motions of cilia, hairlike projections that line the inner surface of the oviduct. It takes about three days for the ovum to travel the entire length of the oviduct to the uterus, and since the ovum only remains fertilizable for twelve to twenty-four hours, successful fertilization must occur in the oviduct.


Upon reaching the ovum, the sperm must first penetrate two layers surrounding it. The outermost layer, called the corona radiata, consists of cells that break away from the ovary with the ovum during ovulation; the innermost layer, the zona pellucida, is a clear, jellylike substance that lies just outside the ovum cell membrane. Penetration of these two layers is accomplished by the release of enzymes carried by the sperm. Once through the zona pellucida, the sperm are ready to fertilize the ovum.


Fertilization occurs when a sperm fuses its membrane with the membrane of the ovum. This act triggers a protective change in the zona pellucida that prevents any additional sperm from reaching the ovum and providing it with extra chromosomes. Following fusion of the fertilizing sperm and ovum, the chromosomes of each become mingled and pair up; the resulting one-celled zygote contains a complete set of chromosomes, half contributed by the mother and half by the father.


It is at the moment of fertilization that the sex of the new child is decided. Genetic sex is determined by a pair of chromosomes denoted X and Y. Female body cells contain two Xs, and each ovum produced contains only one X. Male body cells contain an X and a Y chromosome, but each sperm contains either an X or a Y chromosome. Men usually produce equal numbers of X- and Y-type sperm. The sex of the new individual is determined by which type of sperm fertilizes the ovum: If it is a Y-bearing sperm, the new individual will be male, and if it is an X-bearing sperm, the new individual will be female. Since entry of more than one sperm is prohibited, the first sperm to reach the ovum is the one that will fertilize it.


Following fertilization, the zygote or early embryo begins a series of cell divisions while it travels down the oviduct. When it arrives at the uterus about three days after ovulation, the zygote will be in the form of a hollow ball of cells called a blastocyte. Initially, this ball of cells floats in the fluid-filled cavity of the uterus, but two or three days after its arrival in the uterus (five to six days after ovulation), it will attach to the uterine lining. In 2003, researchers made an exciting discovery when they identified how embryos stop and burrow into the lining of a woman’s uterus. A protein, called L-selectin, on the surface of the embryo acts like a puzzle piece when it touches and quickly locks into carbohydrate molecules found on the uterine surface. This implantation process must occur in exact synchrony during a very short time in a woman’s cycle. (If it occurs outside the uterus, usually in one of the Fallopian tubes, then the result is an ectopic pregnancy, which is often a medical emergency.) In the weeks following conception, the cells of the zygote will form the fetus and the placenta, which surrounds and provides nutrients to the fetus. Over the next nine months, the fetus will increasingly take on a human form, developing muscle tissue, bone, organs, and skin. Pregnancy typically lasts for forty weeks from conception until childbirth. .




Complications and Disorders

Three factors limit the time frame in which conception is possible: the fertilizable lifetime of the ovulated ovum, estimated to be between twelve and twenty-four hours; the fertilizable lifetime of ejaculated sperm in the female tract, usually assumed to be about forty-eight hours; and the time required for sperm capacitation, which is one hour or more. The combination of these factors determines the length of the fertile period, the time during which intercourse must occur if conception is to be achieved. Taking the three factors into account, the fertile period is said to extend from forty-eight hours prior to ovulation until perhaps twenty-four hours after ovulation. For example, if intercourse occurs forty-eight hours before ovulation, the sperm will be capacitated in the first few hours and will still be within their fertilizable lifetime when ovulation occurs. On the other hand, if intercourse occurs twenty-four hours after ovulation, the sperm will still require time for capacitation, but the ovum will be near the end of its viable period. Thus the later limit of the fertile period is equal to the fertilizable lifetime of the ovum, minus the time required for capacitation.


Obviously, a critical factor in conception is the timing of ovulation. In a typical twenty-eight-day menstrual cycle, ovulation occurs about halfway through the cycle, or fourteen days after the first day of menstrual bleeding. In actuality, cycle length varies widely from month to month. It appears that generally the first half of the cycle is more variable in length, with the second half more stable. Thus, no matter how long the entire menstrual cycle is, ovulation usually occurs fourteen days prior to the first day of the next episode of menstrual bleeding. Therefore, it is relatively easy to determine when ovulation occurred by counting backward, but difficult to predict the time of ovulation in advance.


Assessment of ovulation time in women is notoriously difficult. There is no easily observable outward sign of ovulation. Some women do detect slight abdominal pain about the time of ovulation; this is referred to as Mittelschmerz, which means, literally, pain in the middle of the cycle. This slight pain may be localized on either side of the abdomen and is thought to be caused by irritation of the abdominal organs by fluid released from the ovary during ovulation. Other signs of ovulation are an increased volume of the cervical mucus and flexibility of the cervix and a characteristic fernlike pattern of the mucus when it is dried on a glass slide. There is also a slight rise in body temperature after ovulation, which again makes it easier to determine the time of ovulation after the fact rather than in advance. It is also possible to measure the amount of luteinizing hormone (LH) in urine or blood; this hormone shows a marked increase about sixteen hours prior to ovulation. Home test kits to detect LH levels are available for urine samples. There are additional signs of the time of ovulation, such as a slight opening of the cervix and a change in the cells lining the vagina, that can be used by physicians to determine the timing and occurrence of ovulation.


Since ovulation time is so difficult to detect in most women on an ongoing basis, most physicians would counsel that, to achieve a pregnancy, couples should plan on having
intercourse every two days. This frequency will ensure that sperm capable of fertilization are always present, so that the exact time of ovulation becomes unimportant. A greater frequency of intercourse is not advised, since sperm numbers are reduced when ejaculation occurs often. Approximately 85 to 90 percent of couples will achieve pregnancy within a year when intercourse occurs about three times a week.


Couples often wonder if it is possible to predetermine the sex of their child by some action taken in conjunction with intercourse. Scientists have found no consistent effect of diet, position assumed during intercourse, timing of intercourse within the menstrual cycle, or liquids that are introduced into the vagina to kill one type of sperm selectively. In the laboratory, it is possible to achieve partial separation of sperm in a semen sample by subjecting the semen to an electric current or other procedure due to the physical difference of X- and Y-containing sperm. The separated sperm can then be used for artificial insemination (the introduction of semen through a tube into the uterus). This method is not 100 percent successful in producing offspring of the desired sex and so is available only on an experimental basis.


Some couples have difficulty in conceiving a child, in a few cases as a result of some problem associated with intercourse. For example, the male may have difficulty in achieving erection or ejaculation. The vast majority of these cases are caused by psychological factors such as stress and tension rather than any physiological problem. Fortunately, therapists can teach couples how to overcome these psychological problems.


About 10 to 15 percent of couples suffer from some type of biological infertility—that is, infertility that persists for more than one year when intercourse occurs successfully. In about 10 to 20 percent of the cases of infertility, doctors are unable to establish a cause. About one-third of infertility cases are caused by the female partner's problems, while another one-third of infertility cases are caused by the male partner's problems. The remaining cases of infertility are caused by both male and female problems or are unexplained..


In men, the most commonly diagnosed cause of infertility is low sperm count. Sometimes low sperm count is caused by a treatable imbalance of hormones. If not treatable, this problem can sometimes be circumvented by the use of pooled semen samples in artificial insemination or through in vitro fertilization. In vitro fertilization may also be a solution for men who produce normal numbers of sperm but whose sperm lack swimming ability. Another cause of male infertility is blockage of the tubes that carry the semen from the body, which may be caused by a previous infection. Surgery is sometimes successful in removing such a blockage. Another problem, called varicocele, occurs when the veins on the testicle are too large or do not properly circulate blood. This causes the testicles to overheat, which may affect the number or the viability of the sperm. Varicocelectomy, the surgical correction of this problem, may be performed on an outpatient basis.


In women, a common cause of infertility is a hormonal problem that interferes with ovulation. Polycystic ovarian syndrome (PCOS) is a hormone imbalance that affects normal ovulation and is the most common cause of female infertility. Women with PCOS typically have high levels of androgens and many ovarian cysts. Treatment with one of a number of so-called fertility drugs may be successful in promoting ovulation. Clomiphene, a selective estrogen receptor modulator (SERM), is the most commonly prescribed fertility medication. Fertility drugs, however, have some disadvantages: They have a tendency to cause ovulation of more than one ovum, thus raising the possibility of multiple pregnancy, which is considered risky; and they may alter the environment of the uterus, making implantation of a resulting embryo less likely. Therefore, other causes of infertility, both male and female, should be ruled out before fertility drugs are used.


Another common cause of female infertility is blockage of the oviducts or the fallopian tubes resulting from scar tissue formation in the aftermath of some type of infection or prior surgery. Because surgery is not always successful, this condition may require the use of in vitro fertilization or the new technique of surgically introducing ova and sperm directly into the oviduct at a point below the blockage. Another cause of female infertility is an abnormally shaped uterus, which may interfere with the fertilized egg's ability to attach to the uterine wall. Uterine fibroids, noncancerous growths in the uterus, are very common among women and most often cause no symptoms; however, in certain cases, uterine fibroids can make it difficult for the fertilized egg to attach to the uterine wall. Surgery may be performed to shrink or remove the fibroids.


Finally, some cases of infertility result from biological incompatibility between the man and the woman. It may be that the sperm are unable to penetrate the cervical mucus, or perhaps that the woman’s immune system treats the sperm cells as foreign, destroying them before they can reach the ovum. Techniques such as artificial insemination and in vitro fertilization offer hope for couples experiencing these problems.




Perspective and Prospects

For most of history, the events surrounding conception were poorly understood. For example, microscopic identification of sperm did not occur until 1677, and the ovum was not identified until 1827 (although the follicle in which the ovum develops was recognized in the seventeenth century). Prior to these discoveries, people held the belief espoused by early writers such as Aristotle and Galen that conception resulted from the mixing of male and female fluids during intercourse.


There was also confusion about the timing of the fertile period. Some early doctors thought that menstrual blood was involved in conception and therefore believed that the fertile period coincided with menstruation. Others recognized that menstrual bleeding was a sign that pregnancy had not occurred; they assumed that the most likely time for conception to result was immediately after the menstrual flow ceased. It was not until the 1930s that the first scientific studies on the timing of ovulation were completed.


Since there was little scientific understanding of the processes involved in conception, medical practice for most of human history was little different from magic, revolving around the use of rituals and herbal treatments to aid or prevent conception. Gradually, people rejected these practices, often because of religious teachings. By the twentieth century, conception had been established as an area of intense privacy, thought by physicians and the general public to be unsuitable for medical intervention.


In the early part of the twentieth century, the role of physicians in aiding conception was mostly limited to educating and advising couples finding difficulty in conceiving. There were few techniques, other than artificial insemination and fertility drug treatment, available to assist in conception at that time.


The situation changed with the first successful in vitro fertilization in 1978. This event ushered in an era of intense medical and public interest in assisting conception. Other methods to aid conception were soon introduced, including embryo transfer, frozen storage of embryos, and surgical placement of ova and sperm directly into the oviduct.


Paralleling the development of these techniques has been demand on the part of society for medicine to apply them. In most developed countries, infertility rates have been gradually increasing. One reason for increased infertility has been the increasing age at which couples decide to start a family, since the fertility of women appears to undergo a decline past the age of thirty-five. Another factor affecting fertility rates of both men and women has been an increased incidence of various sexually transmitted diseases, which can result in chronic inflammation of the reproductive organs and infertility caused by scar tissue formation.


People’s attitudes toward medical intervention in conception have also changed. The earlier taboos against interference in conception have been somewhat relaxed, although some individuals still do not approve of certain methods of fertility management. Although there remain ethical issues to be resolved, the general public seems to have accepted the idea that medicine should provide assistance to those who wish to, but cannot, conceive children.




Bibliography


Doherty, C. Maud, and Melanie M. Clark. Fertility Handbook: A Guide to Getting Pregnant. Omaha, Nebr.: Addicus Books, 2002.



Harkness, Carla. The Infertility Book: A Comprehensive Medical and Emotional Guide. Rev 2d ed. Berkeley, Calif.: Celestial Arts, 1992.



"Infertility." Medline Plus, February 26, 2012.



"Infertility Fact Sheet." US Department of Health and Human Services—Office on Women's Health, July 16, 2012.



"In Vitro Fertilization (IVF)." Medline Plus, February 26, 2012.



Jones, Richard E., and Kristin H. Lopez. Human Reproductive Biology. 4th ed. Burlington, Mass.: Academic Press/Elsevier, 2013.



Kearney, Brian. High-Tech Conception: A Comprehensive Handbook for Consumers. New York: Bantam Books, 1998.



"Pregnancy: Condition Information." Eunice Kennedy Shriver National Institute of Child Health and Human Development, April 3, 2013.



Weschler, Toni. Taking Charge of Your Fertility. Rev. ed. New York: Collins, 2006.



Wisot, Arthur L., and David R. Meldrum. Conceptions and Misconceptions: The Informed Consumer’s Guide Through the Maze of In Vitro Fertilization and Other Assisted Reproduction Techniques. 2d ed. Point Roberts, Wash.: Hartley & Marks, 2004.

Tuesday 19 December 2017

What was the role of industrial development in creating a social and industrial motivation to go to World War One?

Industrialization during the 19th century created a number of radical changes in human society. Populations grew rapidly even as standard of living rose, something that had essentially never happened before 1700.

Yet with change always comes turmoil, and even countries that didn't undergo outright revolution (as Russia did partway through the war) still had to deal with enormous shifts in the structure of their society and new tensions, especially the tension between workers and capital owners. This could have created conditions more prone to war, as countries were unstable and prone to violence in general.

Improvements in technology were by no means limited to civilian applications, and in the early 20th century weapons technology became extremely advanced, and capable of vastly more destruction than ever before. We now think of tanks and machine guns whenever we think of war; but in that period tanks and machine guns were radical new technologies unlike anything the world had ever seen. (Watch a video of a laser cannon on an experimental destroyer vaporizing an autonomous drone, and you may have some sense of how it felt looking at a machine gun in the 1910s.)

This increased military technology made war mobilization much faster, which could have contributed to causing the war. If deployment takes weeks or months, you can wait for an enemy to start to deploy before you respond. But if deployment takes days or even hours, you can't afford to wait; you need to be ready to deploy immediately or even pre-emptively. This meant that there was less margin for error in diplomacy and more paranoia between leaders. You can think of it as the difference between everyone in a room having a sword at their hip versus everyone in a room having a gun pointed at someone else's head. The latter scenario is obviously a lot more volatile. (This is the reason I don't believe nuclear weapons are actually a useful deterrent, by the way.)


The industrialization of war was also the beginning of the military-industrial complex, where corporations that manufacture military equipment now have an economic incentive to pressure the world into war. Previously, war was mainly a question of "labor", i.e. having enough soldiers; but now it became mainly a question of capital---having the best guns. Corporations that profit from war could put pressure on governments to go to war unnecessarily (though how much this actually has an effect has never been clearly demonstrated).


Yet, it's unclear how much this new technology actually contributed to causing the war. It's important to note that war has been part of human life for all of recorded history, and organized homicide is part of the behavioral profile of all primates going back millions of years. What made WW1 unique was not the fact that war happened or even the proportional death toll; it was mainly the fact that world population was so large and so well-organized, making what would otherwise have been dozens of wars around the world killing hundreds of thousands of people out of hundreds of millions into a single global war that killed millions of people out of two billion. Total global rates of death due to violence have been declining for centuries, and WW1 and WW2 were spikes in the trend that don't change the overall pattern.

In this sense, industrialization did cause WW1, not because it made the war happen or even made it that much worse, but because it made more people in the world and united people into nations. Prior to the 18th century the modern nation-state really didn't exist, and even well into the 19th century it was not the leading mode of political organization; so wars inherently had to be over smaller regions---but there were so many small wars that the total rate of death was actually higher, not lower. The huge absolute figures for deaths in the World Wars are really due to the very high population growth during the 19th and 20th century, not a sudden unique surge in violence. (Which is more violent, a city with 1 million people and 100 murders, or a city with 100,000 people and 20 murders? Clearly the latter, right?)

What is drugged driving? |


Statistics

Drugged driving has become a growing problem in the United States and across the globe; twenty-first-century rates in the United States approach those of drunk driving, and the US Centers for Disease Control and Prevention estimates that 18 percent of vehicle accidents annually are related to drugs. Data collected by survey and reporting organizations, such as the Fatality Analysis Reporting System and the Monitoring the Future drug-use survey in teenagers, suggest that drugs are identified seven times more often than alcohol in youth drivers on weekend nights.




Nearly one-third of high school seniors admit to riding with an impaired driver or driving a car while impaired from drug use. Marijuana is the primary drug associated with drugged driving in youth and all other age groups; the second and third most frequently used are cocaine and methamphetamines, respectively.


A growing concern is the contribution of prescription painkillers and sedatives to drugged driving. In the United States, impaired driving rates from benzodiazepines or opiates approach those of drugged driving with cocaine.




Risk Groups

People age fifty-five years and older are at particular risk of impaired driving from the sedating effects of prescription drugs through normal use or misuse. Any person who uses a sedating prescription or nonprescription drug may experience impaired driving; people who obtain multiple prescriptions of painkillers, sedatives, or antidepressants are most likely to experience drug misuse and driving impairment.


The most common drugged-driving risk group, however, is youth, especially new drivers. Approximately 25 percent of vehicle-related fatalities that occur each year involve drivers younger than age twenty-five years. Prior offenders of drunk or drugged driving laws comprise another at-risk population.




Testing

Documenting drugged driving is complicated, in part because impairment thresholds are frequently unknown and evaluation methods are not standardized. For example, studies show that marijuana and stimulants increase the likelihood of poor decision-making and response times while driving. Connecting the use of these drugs with specific vehicle crashes is difficult, however, because of overlapping use, low testing rates, and poor understanding of the behaviors that cause reckless driving. Better and more frequent drug testing can support the connection between drug use and impaired driving.


Testing for drug impairment is more complex than testing for blood alcohol content (BAC). Choices about what drugs to test for and what methods to use remain unclear. Because drug levels in the body fluctuate nonlinearly, tested concentrations are not always predictive of effect. In addition, circulating drug metabolites can impair ability at least as much as the original drug but may not affect test results. Finally, drug testing must be conducted rapidly, because the primary drug can dissipate within hours despite lingering impairment.


Testing can be performed on urine, blood, or oral fluids. Blood tests report the most accurate drug concentrations but are invasive, costly, and time consuming. Urine is less indicative of drug effects and is difficult to test reliably in the field. Both blood and urine testing can require offsite laboratory evaluation, which adds to the cost and timeliness of results.


Oral fluid testing, conversely, is easy to administer and provides reasonable accuracy. However, these tests still do not evaluate metabolites, and they do not always have evidence-based cut points that reflect impairment. Oral kits have become preferred for field use because they are rapid-use tests that do not require a laboratory. Although rapid tests provide the best option for identifying drugged drivers quickly and are more accessible for law enforcement, they have lower sensitivity and more false positives than laboratory tests.


A barrier to frequent drugged-driving testing is appropriate drug identification. Law enforcement must identify behaviors representing drug use before ordering tests; the ability to distinguish the types of drugs by symptoms is crucial to minimize what drugs are tested for. Drug-recognition-expert programs are being developed to address this need and to educate law enforcement officers about the symptoms of specific drug use.




Prevention

Prevention is implemented through the education of three populations: new drivers, who are often unaware that drugged driving poses risks and consequences similar to those of drunk driving; law enforcement professionals, who need to identify and test persons who are suspected of drugged driving; and health professionals, who can identify risks associated with specific prescriptions or persons on multiple high-risk drugs.


A reduction in drugged driving rates and prevention of future offenses requires improved testing technology and application, greater professional education and outreach efforts, and broad public-health awareness campaigns. These efforts can be supplemented by clear legal restrictions, especially zero tolerance policies for illicit drug use while driving. Partnered efforts for public education, especially youth antidrug campaigns, are necessary deterrents, as are fines and arrests for drugged driving.


Over-the-counter and prescription drugs pose a greater challenge for prevention and legislation, as these drugs are legal and common. However, even therapeutic dosages can affect driving in some people. The efforts of health professionals to educate the public about the sedating effects of legal drugs and about the risks of misuse and drugged driving should be at the forefront.




Bibliography


"DrugFacts: Drugged Driving." National Institute on Drug Abuse. NIH, May 2015. Web.27 Oct. 2015.



Institute for Behavior and Health. “Drugged Driving Research: A White Paper.” 31 Mar. 2011. Web. 2 Apr. 2012. http://www.whitehouse.gov/sites/default/files/ondcp/issues-content/drugged-driving/nida_dd_paper.pdf.



Maxwell, J. C. “Drunk Versus Drugged: How Different Are the Drivers?” Drug and Alcohol Dependence 121 (2012): 68–72. Print.



National Institute on Drug Abuse. “What Is Drugged Driving?” Dec. 2010. Web. 2 Apr. 2012. http://www.drugabuse.gov/publications/infofacts/drugged-driving.



Office of National Drug Control Policy. “Teen Drugged Driving Toolkit: Parent, Coalition, and Community Group Activity Guide.” Web. http://whitehouse.gov/ondcp/drugged-driving.

How can a 0.5 molal solution be less concentrated than a 0.5 molar solution?

The answer lies in the units being used. "Molar" refers to molarity, a unit of measurement that describes how many moles of a solu...