THE SECRETION AND PROPERTIES OF MILK 1391 



The caseinogen of human milk presents several points of difference 

 from the caseinogen of cow's milk. It is less easily precipitated by 

 acids. When coagulated by rennet it does not form a firm clot, but is 

 thrown out in a flocculent form. It is thus much more susceptible to 

 the action of gastric juice. Whereas the caseinogen of cow's milk 

 generally gives a precipitate of ' pseudonuclein ' on digestion with 

 pepsin and hydrochloric acid, a smaller or no precipitate is formed 

 with human caseinogen. 



Another important advantage of human milk for the infant lies in 

 the presence of antitoxins. It has been shown by Ehrlich that when 

 a female animal has been immunised against any toxin and has pro- 

 duced in consequence antitoxins in its blood, these antitoxins will, 

 if it has young, pass over into the milk. The same passage of anti- 

 bodies into the milk has been proved in the case of various infective 

 disorders. The ingestion of human milk will therefore not only 

 nourish the infant, but will provide it with a certain measure of passive 

 immunity against possible infection by diseases to which its species is 

 liable. 



THE SECRETION OF MILK. When fully formed, each mam- 

 mary gland consists of fifteen to twenty lobes connected by connective 

 tissue. Each lobe is made up of a mass of secreting alveoli which lead 

 by narrow ducts into one large lactiferous duct. These lactiferous 

 ducts, one from each lobe, open on the nipple, undergoing in the nipple 

 itself an oval enlargement. Before secretion begins the alveoli as well 

 as ducts are lined with a cubical epithelium. When secretion com- 

 mences a marked difference develops between the epithelium of the 

 alveoli and that of the ducts. While the latter retains its previous 

 character, the cells of the secreting epithelium grow in length and pro- 

 ject into the lumen of the gland. In the innermost part of the proto- 

 plasm numerous fat globules make their appearance. If sections 

 be made of the gland during the various stages of its activity and 

 stained by Altmann's method (acid fuchsin and picric acid), it will 

 be seen that the commencement of activity is marked by the growth 

 of the innermost part of the cells and the development in these of 

 a number of granules (Fig. 564). These granules finally lengthen 

 into shapes like spirilla, while others of them form fat and become 



