THE SECRETION AND PROPERTIES OF MILK 1243 



to digest, and often teeming with micro-organisms. There is no doubt that 

 of the children dying during the first year of life four-fifths are murdered by 

 this unnatural method of feeding. In some cases it is necessary to adopt 

 artificial feeding because the mother is abnormal, and there is an insufficient 

 secretion of milk. It is therefore important to know what are the main differ- 

 ences in composition between human and cow's milk. In human milk the 

 caseinogen is not only absolutely but also relatively less than in cow's milk, 

 while the latter is relatively poorer in milk sugar. Human milk is poorer 

 in salts, especially in lime, containing only one-sixth of the amount present in 

 cow's milk. Human milk is also said to be poorer in citric acid. The main 

 differences may be summarised as follows : 



The caseinogen of human milk presents several points of difference from 

 the caseinogen of cow's milk. It is less easly 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 produced in conse- 

 quence 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 mammary 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 epithe- 

 lium. When secretion commences 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 j ec t into the lumen of the gland . In the innermost part of the protoplasm 

 numerous fat globules make their appearance. If sections be made of the 



