A fact of importance is that the fresh milk has physiological prop erties;—that it contains an oxidizing, fat-splitting enzyme, and even other properties which are destroyed by boiling.
The Beginning of the Activity of the mam mary glands belong to those peculiar organs which functionate only periodically. The question now' arises, What is the special stimulus which starts the secretion? Without considering the many more or less impossible theories, that of von Halban deserves the greatest consid eration. According to this author, the expulsion of the placenta, which during pregnancy has a proliferating and tonic influence upon the breast-glands, gives rise to the secretion. The formation of the milk depends without doubt upon the influence of the nervous system, but the more intimate connection has not yet been determined.
What Starts the Secretion milk-glands are stimulated to activity by reflex action. The necessary stimulus is the act of nursing. In the first days, only a small quantity, and that colostrum, is secreted; rapidly the daily amount increases, until after a few weeks the acme is reached. The secretion remains in this condition, with slight varia tions, for months, almost always adapted to the needs of the child, which thrives for a long time on the same quantity of nourishment. The absolute requisite for the proper normal condition is that the act of sucking should affect the breasts amply and continuously. If this is unsatisfactory, when for example the child is weak or the mother is in poor condition, there is either a lack of development or a premature cessation of the supply of milk; only by diligent application of the child to the breast is it possible to secure the best that the breast is capable of producing.
The functional capacity remains at its height only when the breast is regularly and completely at least four or five times a day. Obstruction should by no means be allowed to occur. As soon as a stasis in the milk stream occurs the phenomenon of involution sets in, which manifests itself by the immediate appearance of colostrum corpuscles (described above as fat-laden leucocytes), which return the fat from the glands back into the circulation. After nursing has been discontinued
for a few days the secretion practically disappears; frequently, however, it happens that even after a longer pause it is possible to secure the return of the secretion.
Evacuation of the complete emptying of the milk-glands is procured only by the nursing child; no other means can secure this result, as is possible in the cow. It is impossible either with the breast-pump or by the most thorough manipulations. Often a strong child nurses easily oven after the pump or the hand is not able to secure another drop. The breast-pump is especially inefficient, but like all mechanical contrivances it has the advantage of relieving one of the necessity for personal dexterity. By proper manipulation with the hand it is very often possible to relieve the breast to a great ex tent. One must remember, however, that it is unnecessary to compress the whole breast, it being sufficient. to manipulate that part covered by the areola, at the same time drawing the whole breast forward and downward, ceasing momentarily, then repeating this manoeuvre. The effect is, as a glance at Fig. 51 shows, that the galactifcrous sinus is first emptied, then with relaxation of the pressure is again expanded by the action of the surrounding connective tissue, and draws the milk from the more remote parts. This procedure is aided by the general com pression of the organ, which is produced by the tense skin in drawing it forward. Individual limitations are very great, of course, and many women can press out the milk far better than can others.
Individual Differences in Function.--The deviation from the normal- type in the gland function is of relative frequency. It is of im portance to know that only slowly and with difficulty can many breasts be brought to their highest point of activity. In these cases it is neces sary to have some strong and continuous nursing stimulus in order to secure the result. Again, it is significant that many breasts give out their milk more easily than do others, and that this occurs with the slightest exertion of the child.