CHAPTER II
SWEAT-PORES, RIDGES AND FURROWS
Section of Skin, showing Sweat-Glands, Ducts and Pores
a. pore open.
b. pore closed.
d. sweat duct.
e. sweat gland.
The front or palmar surface of human hands, and the corresponding solar or plantar surface of the feet, are marked with alternate ridges and furrows, lying for the most in nearly parallel rows, but often again at certain points on palm or sole, curving, splitting, twisting, or joining to form patterns of much intricacy. The ridges, called technically rugæ (sing. ruga), are punctuated at very frequent intervals with small openings, which are the mouths or pores of the sweat ducts connected with certain glands which lie deep in the lower strata of the skin. The furrows or sulci (sing. sulcus) are almost devoid of any such apertures. There are probably some two or three millions of those tiny sweat pores in a human body, which afford an evaporating surface, according to the anatomist Krause, of about eight square inches. The sweat is a watery, slightly saline fluid, with slight—very slight—traces of grease, some small cell-like particles, and some carbonic acid and other gaseous matters, which exhale from the skin. The more oily secretion of the skin comes from a different set of openings with their associated glands, the sebaceous glands, which are associated with the hairy surfaces of the body. In Ludwig Hopf’s work, The Human Species, the subject is discussed fully. When the palmar surface leaves a distinctly greasy impression, this greasiness must have been acquired from outside or from transmitted exudation from the back or dorsal surfaces, or other parts of the body.
Those skin ridges, apart from any relation they may have either to the sweat-pores or to the special nerves of touch and temperature which lie near them, serve a useful purpose in helping the horny hands of toil to grasp its tools firmly. They occur in a few other parts of animals somewhat near to us in the scale of being. A striking example is that on the palmar surface of the prehensile or grasping tail of the Spider Monkey (Ateles ater), which it uses in climbing almost like a hand.
When the ridges in human fingers are well softened with water, and are then rubbed along the surface of a tumbler or wine-glass, musical sounds may be elicited, which are caused by the alternate resistance and yielding of the softened ridges. This was the principle of the “musical glasses” of Goldsmith’s time. The navvy often begins his labours by moistening his loof. After his efforts make him perspire, he has no further need in this way for his salivary resources. Hence Nature, too, has placed the openings of the sweat-pores on the crests of his ridges, and not, as Herbert Spencer on one occasion is said to have supposed she had done, in the troughs of the furrows, where they are very seldom to be found, and would not be nearly so useful. Curiously enough, our modern makers of indiarubber tyres work a trademark pattern or title in ridges on their wares, so as to secure a good grip on the road—and on the market. In a similar way the carriers of Manchuria adorn their clumsy wheels with studs to prevent their skidding.