SECTION V 



THE SECRETION AND PROPERTIES OF MILK 



LACTATION 



DURING pregnancy the foetus obtains the whole of its nourishment 

 from the mother by means of the placenta. After birth the quality of 

 the nutriment supplied to the young child depends on the activity 

 of the cells of the mammary glands. Now, however, nutrition in- 

 volves further activity on the part of the young animal, the alimentary 

 canal being concerned in the digestion of the milk supplied by the 

 mother, and the excretory organs, especially the kidneys , being made 

 use of for getting rid of waste material. The preparation of the 

 mammary glands for the subsequent nourishment of the new-born child 

 begins in the first month of pregnancy, and is marked by swelling of the 

 glands, rapid proliferation of the duct epithelium, and production of 

 many new secreting alveoli. The development of these glands ir^the 

 rabbit has been already described, and there is no doubt that in the 

 human species the process follows very much the same course, being, 

 however, spread over nine months instead of four weeks, as is the case 

 with the rabbit. During the latter half of pregnancy a watery fluid 

 can generally be expressed from the nipple. In certain mammals this 

 watery secretion gives place to a secretion of true milk at the end of 

 gestation or during the process of parturition itself. In the woman the 

 secretion does not begin as a rule until the second or third day after 

 birth, though the formation of milk may be anticipated if a child has 

 been put to the breasts during the latter part of pregnancy. Secretion 

 begins on the second or third day, even if the child has been born dead 

 and no attempt at suckling has taken place. For the maintenance 

 of the secretion the process of suckling is absolutely necessary. If the 

 woman does not nurse her child, the swelling of the breasts gradually 

 passes off, the milk disappears, and the glands undergo a process of 

 involution. Under normal conditions the secretion of milk lasts for 

 six to nine months and may in rare cases extend over more than a 

 year. The amount secreted increases at first with the growth and 

 size of the child. The following Table represents the average amount 

 of milk secreted during the thirty-seven weeks after birth. It will, of 



1384 



