THE INFLUENCE OF NERVES ON SECRETION. 179 tate, are multiple. Exhalations, which mainly occur from serous surfaces, will be hereafter considered; but it may be here stated that, according to Schmidt, their composition varies with the size of the capillaries and quantity of albumen in the blood. The quantity of albumen in some of these fluids is as follows: pleural, 2.85; peritoneal, 1.13; arachnoid, 0-6; areolar tissue, 0.3, in the hundred parts. The nervous system powerfully influences secretion. Both motor and sympathetic filaments can be traced into glands. The motor seems to increase the flow of blood, and thus renders the secretion more abundant; the sympathetic, by constringing the vessels, diminishes the secretion remarkably. The secretion of urine in an hysterical paroxysm, the flow of bile and subsequent diarrhoea by terror, the gush of tears which grief excites, and the production of milk by a mother while in a fit of anger, so hurtful as to poison her offspring, are instances of the influence of innervation on the function of secretion. It has been found that division of the nerves of the kidney which surround the renal artery, produces either suppression of urine or the secretion of a bloody coagulable fluid. We have before mentioned that Bernard discovered that the blood in the veins coming from a gland was scarlet, if the gland was secreting; modena, from being charged with carbonaceous matter, if inactive; and precisely the contrary is the case with muscles. Many secretions have been already, or will be subsequently described, in treating of the function which they subserve; but in the present chapter we will consider milk, as being entirely recrementitious; bile, which is partly so; and urine, which is wholly excrementitious. THE MAMMARY GLAND Consists of tubes, which can be traced from the nipple, where they open by about 20 orifices. At about the areola they dilate into "ampullæ," which in woman hold about a drachm; in cows, constituting the udder, about a quart. The lactiferous ducts then branch into lobules bound together by areolar tissue, and end in cœca, or follicles about ado in diameter. These are lined by epithelium, and are filled with oil-cells during lactation. Amidst the follicles, blood-vessels, lymphatics, and nerves plentifully ramify. The gland is developed, like the sebaceous glands, as an infolding of the skin, and it begins to branch into lobules about the sixth month of intra-uterine life. The male breast remains in a rudimentary condition usually, but Humboldt and others have recorded instances in which milk was secreted by men. Dr. Davys, of Swords, has met with a case (which he has kindly shown me) where the left gland was as large in a healthy man 87 years of age as it usually is in women not suckling. The organ appeared so perfectly formed that it might have secreted milk if excited by the application of a child. The breasts of infants, male as often as female, occasionally secrete a fluid identical with milk. Abnormalities may occur with regard to the number of breasts, as in Dr. Shannon's remarkable case, where there were four, all secreting milk; but entire absence of the mammæ is extremely rare. The nipple is surrounded by the areola, which undergoes definite changes during pregnancy, and possesses muscular tissue, like the ducts, which can alter its direction. In early life it is conical, but after suckling the extremity becomes much enlarged, so that the infant may grasp it more readily. The changes produced by age are described by Sir A. Cooper: "At 16 years, it is slightly wrinkled; at 17, it has small papilla on its surface; from 20 to 40 years, the papilla are larger; from 40 to 50, the nipple becomes wrinkled; from 50 to 60, the nipple is elongated; and in old age it usually has a warty appearance. The Milk, secreted after parturition, is called colostrum, and in it can be seen very large fat-cells, dis covered by Donnè. It has usually a purgative effect on After two or three days, milk assumes its the infant. m Globules of Colostrum and When left still for about six hours, the fat-cells rise to the surface in the form of cream. Each cell has a wall of casein, so that ether will not dissolve out the fat; but, by dissolving this cell-wall by an alkali, or bursting it by churning, the fat can be separated as butter. The casein can be removed from the remaining fluid by acids or rennet, but not by mere heat. The following analyses indicate the composition of milk from two women 22 years of age, and similarly circumstanced as regards time of delivery, diet, &c., only differing in complexion : The proportion of these constituents vary very much throughout lactation, according as the respiratory, plastic, or saline ingredients are required for infant growth. It would appear that there is no casein whatever in colostrum, but instead of it albumen, for it is coagulated by boiling. In about 36 hours, or much less when the weather is warm or the air charged with electricity, casein acts as a catalytic, and changes sugar into lactic acid (C24 H24 O24 = 4 (HO, C5 H5 О5)), which then curdles the milk. The butyrin also throws off butyric acid, which produces the rancid smell. A pure, watery solution of milk sugar will never turn sour, and as it does not undergo alcoholic fermentation at the temperature of the body, no carbonic acid, which would distend the infant's bowels, is produced. Kiestin, which is found in the urine of pregnant women, or when lactation is checked, is composed of casein, butyric acid, and the phosphates. The mammary gland, by a kind of straining, passes through some salts, refuses others. Thus, iodide of potassium if administered can be found in the mother's milk and infant's urine, which is not the case with ferrocyanide of potassium. Gold has been stained with mercury if placed in milk from a woman taking that drug. Quinine is one of the few vegetable substances which pass into milk; yellow, blue, and red tints are occasionally given to it by peculiar fungi. Like other secretions, milk becomes very concentrated during acute inflammations. In phthisis, the water is said to be increased, and the butter decreased to one-third. Blood, pus, and colostrum cells, long after parturition, may occur abnormally. The diurnal quantity of milk secreted by a suckling woman varies much, but averages about 40 ozs. The milk of cows and other animals differs so widely from human milk, and even that of other women so much from that of the mother, and artificial aliments afford so poor a substitute, that we cannot avoid deploring how often previous disease of the mother or the follies of fashionable life deprive the infant of the food designed by nature for it. Such circumstances are prolific causes of that widespread evil-infant mortality. The best substitute for human milk is recommended to be made as follows: Cow's milk, 8 ozs.; cream, 2 ozs.; water, 6ozs.; sugar of milk, oz. (For some remarks on this subject, see my "Lectures on Public Health.") THE LIVER. The liver is remarkable for its size, being the largest gland in the body, for occurring almost universally in lower animals, for intricacy of structure, and for the variety of functions it performs. It weighs about 4lb, or about of the weight of the body, its proportion being very much greater in fœtal life, when also the left lobe is larger than the right. These differences can be accounted for by the circulation through the umbilical vein, here sketched, the course of which is as follows: Diagram to represent the Circulation in Fetal Liver. conducted by the falciform ligament to the under surface of the liver, it sends off many branches to the left lobe, and none to the right, which is altogether supplied by the porta, the left branch of which joins the umbilical vein. The latter vessel then runs back to the cava under the name of ductus venosus, a tube which, like the umbilical trunk, closes after birth, whereas the left branches remain pervious, and carry the blood of the porta. The liver is very vascular, the blood for its nutrition being supplied by the hepatic artery. Around this vessel there entwine several branches from the solar plexus, and the right phrenic nerve also sends branches to the organ |
