analysis was made from milk obtained on the twelfth day after de livery. Human milk has, therefore, more sugar of milk and less cheesy matter than that of the cow; hence it is sweeter; more liquid; less coagulable; and incapable of being made into cheese. It has also albuminous, oleaginous, and saccharine ingredients combined, so as to adapt it admirably for the young as an aliment; and of all the secreted fluids it appears to be most nearly allied to blood in its composition.' M. Romanet has affirmed, that the globules in cow's milk are wholly formed of butter, which exists as a pulp, enveloped in a white, translucent, elastic and resistent pellicle; and that the cyst is broken in churning, by which the butter escapes, and the pellicles floating about separately constitute the white particles that give consistence to buttermilk. When human milk is first drawn, it is of a bluer colour than that of the cow. It rather resembles whey, or cow's milk much diluted with water. If allowed to rest, it separates, like the milk of other animals, into cream and milk,-the quantity of the cream being one-fifth to onethird milk. The milky portion, however, appears semitransparent like whey, instead of being white and opaque like that of the cow. During the first days of its remaining at rest, abundance of cream and a little curd are separated, and lactic acid is developed. The specific gravity of human milk was found by Dr. Rees to be 1.0358, and the solid contents 12 per cent. The specific gravity of the cream is 1.021.3 The quantitative analysis of the colostrum, after the investigations of Simon, Chevallier and Henry, Stipriaan Luiscius, Boussingault and Le Bel are thus given by Professor Scherer:-" Of the 3.1 of fixed salts unalterable by heat, in Simon's analysis, 1.8 part was insoluble in water. Casein the nitrogenized constituent of milk-is distinguished from fibrin and albumen by its great solubility, and by not coagulating when 1 Dr. G. O. Rees, Art. Milk, Cyclop. of Anat. and Physiol., Nov., 1841. 2 Comptes Rendus, Avril, 1842. 3 Sir Astley Cooper, On the Anatomy of the Breast, Amer. edit., p. 83, Philad., 1845. 4 Op. cit., s. 451. heated. This is regarded by Liebig' as "the chief constituent of the mother's blood. To convert casein into blood no foreign substance is required; and in the conversion of the mother's blood into casein no elements of the constituents of the blood have been separated." The quantity and character of the milk differ according to the quantity and character of the food,-a circumstance, which was one of the greatest causes for the belief, that the lymphatics or chyliferous vessels convey to the mammæ the materials for the secretion. The milk is, however, situate in this respect like the urine, which varies in quantity and quality according to the amount and kind of solid or liquid food taken. The milk is more abundant, thicker, and less acid, if the female lives on animal food; and possesses the opposite qualities when vegetable diet is used. It is apt, also, to be impregnated with heterogeneous matters, taken up from the digestive canal. The milk and butter of cows indicate unequivocally the character of their pasturage, especially if they have fed on turnip, wild onion, &c. Medicine, given to the mother, may in this way act upon the infant. Serious-almost fatalnarcotism was induced in the infant of a professional friend of the author, by a dose of morphia administered to his wife. It would seem, that occasionally the secretion of the two glands differs. A case has been related in which the milk of the right breast had a distinctly salt taste, whilst that of the opposite breast was of the ordinary sweetness. A difference also is at times observed in the number and size of the globules of the milk obtained from the two breasts. M. Devergie has found by examination with the microscope, that the milk of women differs not only in respect to the size of the globules, but to the number of these,-a high or low amount of globules indicating richness or poorness of the milk generally. Of 100 nurses, 17 had the large globuled variety; 22 the small globuled; and 61 the medium size. The quantity of milk secreted is not always in proportion to the bulk of the mamma: a female whose bosom is of middle size often secretes more than one in whom it is much more developed; the greater size being usually owing to the larger quantity of adipous tissue surrounding the mammary gland, which tissue is nowise concerned in the function. The ordinary quantity of milk that can be squeezed from either breast at any one time, and which must consequently have been contained in its tubes and reservoirs, is about two fluidounces. The secretion usually continues until the period when the organs of mastication of the infant have acquired the necessary developement for the digestion of solid food; and it generally ceases during the second year. For a great part, or the whole of this time, the catamenia are suspended; and if both the secretions,-mammary and menstrual, go on together, the former is usually impoverished, and in small quantity. This, at least, is the general opinion. Some, however, think, that no general rule can be established on the subject; and that the condition of the child's health ought to be the only guide in regard to weaning, after the recurrence 1 Animal Chemistry, Amer. edit., p. 51, Cambridge, 1842. 2 Mémoires de l'Académie Royale de Médecine, tom. x. Paris, 1843. 1 of the catamenia. M. Gendrin would on no account permit a woman to continue nursing after they had returned. The subject has been investigated by M. Raciborski, who laid the results before the Académie Royale de Médecine, of Paris, in May, 1843. His inferences are, that, contrary to generally received opinion, the milk of nurses who menstruate during suckling does not differ sensibly, in physical, chemical, or microscopic characters, from that of nurses whose catamenia are suspended;-that the only difference, which can be detected between the two kinds of milk, is, that in most cases the milk of menstruating nurses contains less cream during the menstrual periods than in the intervals, which accounts for the bluish appearance occasionally presented by such milk;-and that a nurse should never be rejected merely because she menstruates. Whilst lactation continues, the female is less likely to conceive; hence the importance,-were there not even more weighty reasons,of the mother's suckling her own child in order to prevent the too rapid succession of children. From observations made at the Manchester Lying-in Hospital on one hundred and sixty married women, Mr. Roberton concludes, that in seven out of eight women, who suckle for as long a period as the working classes in England are in the habit of doing about fifteen and a half months on the average-there will be an interval of fifteen months between parturition and the commencement of the subsequent pregnancy; and that, in a majority of instances, when suckling is prolonged to even nineteen or twenty months, pregnancy does not take place till after weaning. In a work on the law of population and subsistence, Dr. Loudon3 lays down the theory, that the laws of nature require lactation to be prolonged for three years; and he expresses an opinion, that the antagonism between the uterus and mammæ is so great as usually to prevent conception in women who have infants at the breast. The opinion does not agree, however, with the facts arrived at by Dr. Roberton, and it is still more opposed to those of Dr. Laycock, who states that 135 married women afforded 209 pregnancies during 766 lactations, or 1 pregnancy in 3.66 lactations, or 27 per cent. The 209 pregnancies occurred in 76 females:that is, 56 per cent. became pregnant whilst suckling; but in 30 of these, pregnancy occurred only once. If the thirty be deducted, there remain 46 or 33.9 per cent., or nearly 1 in 3, who became pregnant on more than one occasion whilst suckling; and 19 of these, or 1 in 7 had always after their first pregnancy-conceived whilst suckling. 4 When menstruation recurs during suckling, it is an evidence that the womb has again the organic activity which befits it for impregna tion. 1 Dublin Medical Press, Aug., 2d, 1843. 2 Edinb. Med. and Surg. Journal, Jan., 1837. 3 Solution du Problème de la Population, &c., Paris, 1842; cited by Dr. West, in Brit. and For. Med. Rev., April, 1844, p. 541. 4 Dublin Medical Press, Oct. 26, 1842. CHAPTER II. FETAL EXISTENCE.-EMBRYOLOGY. WHILST the uterine alterations, which have been pointed out in the last chapter, are taking place, the ovum is undergoing a succession of changes, and the new being is passing through the different phases of intra-uterine existence. The history of these, in the early period, is extremely obscure, owing to the difficult nature of the investigation; and on many deeply interesting points we are compelled to remain in doubt. It is a subject, which has engaged the attention of physiologists of all ages; but it is chiefly to those of more modern times-as Hunter, Cuvier, Dutrochet, Pander, Rolando, Sir Everard Home and Mr. Bauer, Prévost and Dumas, Von Baer, Kuhlemann, Döllinger, Oken, Purkinje, Rathke, C. F. Wolff, Breschet, Burdach, Reichert, Carus, Krause, Seiler, Bojanus, Meckel, E. H. Weber, Bernhardt, Valentin, Coste, Owen, Sharpey, Velpeau, Flourens, Allen Thomson, T. W. Jones, Bischoff, Schwann and Schleiden, J. Müller, Pouchet, Wagner and Martin Barry,-the last two of whom received, about the same time, medals for their researches, the former from the Institute of France; the latter from the Royal Society of London-that we are indebted for our more accurate and precise information. 1. ANATOMY AND HISTOLOGY OF THE FŒTUS. a. Foetal Developement. As the developement of the mammalia greatly resembles that of birds, the histogeny of the impregnated ovum, at the earliest periods, was, until of late years, chiefly studied in the latter; and there can be no doubt as Wagner1 has remarked, that carefully conducted researches on the ovum of these animals are much better calculated to throw light on the developement of the human embryo than any amount of necessarily unconnected observations of human ova aborted at an early period; and, in the majority of cases perhaps, morbid. "Unquestionably," observes Valentin," the class of birds is the centre around which all observations on developement arrange themselves, and this, not so much on account of any grounds intrinsic to this class, as by reason of extrinsic circumstances, which are completely under our control. In no other class of animals do we possess the same facilities of procuring embryos in the various stages of their progress. Nowhere can we multiply and repeat our inquiries to the same extent as here. It was on this account that Fabricius ab Aquapendente began his investigations with the brooded egg, and that Harvey and Malpighi followed in the same course. It was on the egg that Wolff made his im 1 Elements of Physiology, by R. Willis, p. 80, Lond., 1841. portant discoveries in regard to the formation of the intestinal canal, of the blood, of the extremities, and of the kidneys; and it was by the study of the embryo of the common fowl, that Döllinger and his school, in our own day, were enabled to give a permanent foundation to the history of developement as a science. The bird must, therefore, and on these grounds, be made the starting point for all future inquiries, the norma and basis to which insulated facts in the developement of mammalia and man must be referred." It has been well remarked, too, by Wagner,' that whoever would work out a knowledge of the developement of animals generally for himself must begin with the study of the chick, were it only for the reason, that we possess the best descriptive works upon this portion of the subject. The early processes of developement are, indeed, the same in all animals. "The embryos of different animals resemble each other more strongly in proportion as we examine them at an early period. We have already stated, that during almost the whole period of embryonic life, the young fish and the young frog scarcely differ at all; so it is also with the young snake, compared with the embryo bird. The embryo of the crab, again, is scarcely to be distinguished from that of the insect; and if we go still farther back in the history of developement, we come to a period when no appreciable difference whatever is to be discovered between the embryos of the various departments. The embryo of the snail, when the germ begins to show itself, is nearly the same as that of a fish or a crab. All that can be predicted at this period is, that the germ, which is unfolding itself, will become an animal: the class and group are not yet indicated."2 The egg of a bird-of a hen, for example-consists of two descriptions of parts,-the one comprising those that are but little concerned in the developement of the new being;-the other those that remain after the chick is hatched,-as the shell and the shell membrane which lines it; and those that undergo changes along with the chick, and cooperate in its formation, as the white, the yolk, and the cicatricula, macula, tread or gelatinous molecule as it was formerly termed—which includes the germinal vesicle or Purkinjean vesicle, and the germinal or germ spot of later observers. When the ovule quits the ovary, it consists only of the yolk and its investing membrane:-with the germinal, vesicle and germinal spot. (See Figs. 384 and 385.) The yolk serves the same purpose for the animal as the amylaceous and oily matter in the seed serves for the plant. It is the nutriment on which the embryo subsists, until it is capable of obtaining it in another manner. On this yolk is the cicatricula, consisting, as has been said, of a nucleated cell, of which the germinal spot is the nucleus, the germinal vesicle the cell. In its passage through the oviduct, the ovule receives the albumen or white of egg, the purpose of which is to serve as nutriment; for it is gradually taken up as the yolk is exhausted. This is deposited upon the surface of the ovule; and from the blood vessels of the lining of the oviduct 1 Op. cit. 2 Agassiz and Gould, Principles of Zoology, part 1, page 123, Boston, 1848. |