Sudoriferous glands: In the middle of each of the transverse furrows between the papillæ, and irregularly scattered between the bases of the papillæ in those parts of the surface of the body in which there are no furrows between them, are the orifices or ducts of the sudoriferous, or sweat glands, by which it is probable that a large portion of the aqueous and gaseous materials excreted by the skin are separated. Each of these glands consists of a small lobular mass, which appears formed of a coil of tubular gland-duct surrounded by blood-vessels and imbedded in the subcutaneous adipose tissue. From this mass the duct ascends, for a short distance, in a spiral manner through the deeper parts of the cutis, then passing straight, and then sometimes again becoming spiral, it runs through the cuticle and opens by an oblique, valve-like apparatus. The sudoriferous glands are abundantly distributed over the whole surface of the body; but are especially numerous, as well as very large, in the skin of the palm of the hand. They are estimated from 2,738 to 3,528 in each superficial square inch. They are almost equally abundant and large in the skin of the sole. The glands by which the peculiar odorous matter of the axilla is secreted form a nearly complete layer under the cutis, and are like the ordinary sudoriferous glands, except in being larger and having very short ducts. In the neck and back, where they are least numerous, the glands amount to 417 on the square inch. The total number is estimated, at 2,381,248; and supposing the orifice of each gland to present a surface of 1⁄54 of a line in diameter (and regarding a line as equal to 1⁄10 of an inch) the whole of the glands would present an evaporating surface of about eight square inches.
Sebaceous glands secrete a peculiar fatty matter. Like the sudoriferous glands, they are abundantly distributed over most parts of the body.
The quantity of matter which leaves the human body by way of the skin is very considerable. It is estimated that while 7 grains pass through the lungs per minute, as much as 11 escape through the skin. The amount varies extremely. It is calculated that the total amount of perspiration excreted from the whole body in 24 hours might range from 2 to 20 kilos.
The total amount of perspiration is affected not only by the condition of the atmosphere, but also by the nature and quantity of food taken, the amount of fluid drunk, and the amount of exercise taken. It is also influenced by the mental condition, by medicines and poisons, by disease, and by the relative activity of the other excreting organs, more particularly the kidneys.
The fluid perspiration or sweat, when collected, is found to be a clear colorless fluid, with a strong and distinctive odor varying according to the part of the body from which it is taken. Besides accidental epidermic scales, it contains no structural elements. Its reaction is generally acid, but in cases of excessive secretion may become alkaline. The average amount of solids is about 1.81 per cent, of which about two-thirds consists of organic substances. The chief normal constituents are (1) sodium chloride (common salt), with small quantities of other inorganic salts; (2) various acids of the fatty series, such as fermic, acetic, butyric acid, with probably other acids—CH2O2-C2H4O2—C4H8O2; (3) neutral fats and cholestrine; (4) ammonia (NH3) (urea), and possibly other nitrogenous substances.
The average loss by cutaneous and pulmonary exhalation in a minute is from 17 to 18 grains; the minimum, 11 grains; the maximum, 32 grains; of the average 18 grains 11 pass by the skin and 7 by the lungs. The maximum loss by exhalation, cutaneous and pulmonary, in twenty-four hours is about 3¾ pounds; the minimum, about 1½ pounds. Valentine found the whole quantity lost by exhalation from the respiratory and cutaneous surfaces of a healthy man who consumed daily 40,000 grains of food and drink to be 19,000 grains, or 2½ pounds. Subtracting from this, for the pulmonary exhalation, 5,000 grains, and for the excess of the weight of the exhaled carbonic acid over that of the equal volume of the inspired oxygen, 2,256 grains, the remainder, 11,744 grains, or nearly 15⁄7 pounds, may represent an average amount of cutaneous exhalation in a day.
The Kidneys, two in number, are excretory organs. They are deeply seated in the lumbar region, one on each side of the vertebral column, at the back of the abdominal cavity, and behind the peritoneum. The kidneys measure about 4 inches in length, 2½ inches in breadth, and 1½ inches in thickness. The left is usually longer and narrower than the right one. The weight of the kidney is usually stated to be about 4½ ounces in the male and somewhat less in the female.
The excretory apparatus consists of fine tubules (the tubuli urineferi), malpighian bodies, blood-vessels, nerves, and lymphatics, etc.
The kidneys are highly vascular, and receive their blood from the renal arteries, which are very large in proportion to the organ they supply. Each artery breaks up into four or five branches, these again subdivide and break up into capillaries in the substance of the kidney. The veins arise by numerous venous radicals from the capillary network of the kidney, as seen near the surface of the gland, and collect the blood from the capillary plexus around the convoluted tubules which mainly compose this part, the smaller veins joining together and ultimately forming a single vein and ending in the inferior vena cava.
The kidneys are so arranged by their anatomical structure—that of the cortical and medullary substance, the tubuli urineferi, pyramids, malpighian bodies, etc.—that they separate from the blood the solids in a state of solution. The secretion takes place by the agency of the gland cells, and equally in all the parts of the urine tubes. The protoplasmic cells which line at least a large portion of the tubuli urineferi elaborate from the blood certain substances, and discharge them into the channels of the tubules. All parts of the tubular system of the kidney take part in the secretion of urine as a whole, but there is another provision of vessels for a more simple draining off of the water from the blood when required.