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Clearly the sweat in those two examples not only differs enormously in quantity, but also in quality. And therein lies what we might call the physio-psycho-socio-economic truth about sweat in late 20th century American society: It's more often produced by tension and anxiety—call it psycho sweat—or by voluntary recreational exertion—call it sport sweat—than it ever is by the actual jobs we do. Here we could launch into a discussion of the honesty of our society as mirrored in the honesty of our sweat, but let's skip the sociobabble over the moral function of our sweat glands and move smartly on to the physiological.
Now this is a subject of far more complexity and seriousness than one might imagine after a lifetime of hearing TV hucksters reduce the subject of human perspiration to alarm about underarm odor. Sweat—its causes, purposes and effects—is one of man's oldest concerns. Hippocrates, the 5th century B.C. Greek physician, knew that skin gave off an invisible vaporous substance, but he couldn't explain why or how. Nor did he realize that these vapors were closely linked to fluid sweat, the functions of which he understood remarkably well. Not until the great medico and student of anatomy, Galen, tackled perspiration in the 2nd century A.D. in Rome was the mystery of sweat partially unveiled. Having already stunned the medical heavies of his day with the discovery that the arteries are filled with blood, not air as was widely believed, Galen then revealed that the mysterious vaporous secretion was discharged continuously and involuntarily through the skin and respiratory orifices as "insensible perspiration" and that it took the form of a visible fluid, sweat, when the body heated up beyond a certain point.
After Galen's breakthrough, 15 centuries elapsed before anyone added anything markedly new about sweat. Then, in the 17th century, Sanctorius, an Italian physician, built a large metal arm balanced on a fulcrum. He placed weights equal to his body weight on one end of the arm and sat on a platform on the other end for hours at a time—his slow ascension proving beyond doubt that his body was losing weight through so-called "insensible perspiration." Sanctorius continued to perfect and expand on this experiment for 30 years. In 1687, Marcello Malpighi of Rome established the existence of the orifices in the skin, the pores, from which watery droplets flowed. In 1833, Jan Evangelista Purkinjé of Bohemia discovered sweat glands and their spiral ducts, and in 1922, Use Schiefferdecker of Germany determined that there are two kinds of sweat glands—the eccrine and the apocrine."
A Nobel Prize has never been awarded for scientific work on perspiration, but if there was ever a worthy candidate, it was the late Japanese physiologist Yas Kuno. After 30 years of intense experimentation and investigation with the loyal assistance of some 65 collaborators and technicians, Kuno published in 1956 a 416-page book entitled Human Perspiration. Though a portion of its contents has been proved erroneous by subsequent research, Human Perspiration ranks as the definitive work on sweat. As Kuno wrote of his years of work, "With regard to the study of perspiration, these three decades may rather be looked upon as a period of renaissance."
According to Kuno, "All the daily sweatings in man may be classified into two groups, the thermal and the mental or emotional sweating. Thermal sweating appears over the whole body surface with the exception of the palms and soles. Mental or emotional sweating usually apppears restrictedly on the palms, soles and axillae [the armpits]—although occasionally on other regions as well."
Also, according to Kuno, women generally sweat less than men, people who live in the tropics are able to sweat more than others, and "athletes perspire more easily and more profusely than untrained people, and this seems to be true also of workmen in hot mines or hot factories."
Moreover, according to Kuno, no animal sweats as efficiently as man: "The development of sweat glands and of the associated nervous apparatus has been most highly attained in man, so that human beings stand at the top of the animal kingdom in their ability to keep body temperature constant."
The human nervous and hormonal systems are so sensitive that changes of as little as .1° centigrade trigger the mechanisms, like sweat, that cool or heat the body. The basic, most critical function of sweat is its thermal action, the simple act of cooling the body when it becomes too hot, either because of high external temperatures or from physical exertion. As Kuno wrote, man has by far the most finely tuned cooling system of all mammals, which as a class have the most sophisticated such systems in nature. Even those animals that also have sweat glands—such as the horse, sheep, goat and monkey—don't have as well developed a heat-control apparatus as humans do. On a hot day, sweating animals will have higher body temperatures than usual—will be running fevers, in effect—because their sweat glands aren't capable of pouring out the vast quantities of water needed to hold their body heat at a constant, normal level.
Most mammals rely either on panting or heavy salivation to keep themselves cool. Instead of sweat glands, a dog has a relatively large mouth and tongue; moisture evaporates from the tongue and from the lungs through extra quick and heavy breathing. Lions and tigers routinely increase their respiratory rate from 10 breaths a minute on cool days to 80 or more in the heat of summer. Mice, which have small mouths and no sweat glands, cool off by first drooling saliva on chest and paws and then rubbing it over the rest of their bodies. Elephants, with a huge sweatless body and a small mouth that allows neither heavy panting nor much salivation, keep cool by loading up their trunks with water and squirting it all over themselves—a procedure that probably equals the human sweat system in efficiency, and certainly beats it hands down as an all-round fun cooling method.
Nonetheless, the human perspiratory system is enormously sophisticated and terrifically effective in comparison to all others. The skin is, in fact, the largest organ of the human body. And the skin is absolutely peppered with pores, which are mainly orifices for sweat glands.