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 involves 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 newborn 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 in 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 gesta- 

 tion 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 bom 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 Table on p. 1290 represents the 

 average amount of milk secreted during the thirty-seven weeks after birth. 

 It will of course be greater with strong big children, and smaller with 

 weakly children. 



COLOSTRUM. Before the secretion of true milk begins, the fluid which 



1289 



