PHYSIOLOGICAL CHEMISTRY 325 



condensed milk diluted in suitable proportions, such a 1 in 12 to begin 

 with, forms a good inexpensive substitute for human milk. 



But when these alterations have been made in cow's milk it has only 

 the same percentage composition and certain well-marked differences 

 must be pointed out. Such differences are : 



(1) The proportion between the amount of the different kinds of 

 protein in cow's and human milk. 



Cow's milk, 3*02 per cent, caseinogen, '53 per cent, lactalbumin. 

 Human 1-00 '50 



It will be seen that human milk contains relatively far more lact- 

 albumin than does cow's milk, so that even when cow's milk is diluted 

 there is the discrepancy between the relative amount of the proteins 

 to be taken into account. It is stated that if lactalbumin be added to 

 diluted cow's milk it causes it to yield the same light form of clot as 

 does human milk. It is also interesting to note that the first secreted 

 milk, colostrum, is very rich in lactalbumin. 



(2) The caseinogens of the two milks are not of the same composition 

 either in percentage or actual composition. It has recently been shown 

 that a carbohydrate group is attached to the caseinogen of human 

 milk, such a group is absent from that of cow's milk. 



(3) The percentage of the salts present differs in the two milks 

 cow's milk contains more calcium, iron and phosphoric acid; human 

 milk more potassium and chlorine. 



(4) There is a provision in the mother's milk of protective bodies for 

 her offspring. Perhaps the strongest argument for the human mother 

 to nurse her child wherever it is possible, is shown by the "changeling 

 experiments " of Ehrlich. This eminent researcher performed the fol- 

 lowing remarkable experiments. He immunised a male and a female 

 mouse to the poison abrin before they were allowed to reproduce. 

 He then crossed the immunised male with a non-immunised female, 

 and the immunised female with a non-immunised male. Upon 

 the birth of the young, it was found that those of the immunised 

 female possessed an immunity to the poison, which increased after birth, 

 and was therefore not derived from the placenta alone ; whereas the 

 young of the non-immunised female that is, of the immunised male 

 possessed no immunity towards the poison. The families were now 

 changed over, the immunised mother suckling the non-immune young, 

 and vice versa. It was then found that the once non-immune young 

 acquired an immunity, whereas the immune-born young quickly lost 

 theirs. These results are all the more remarkable, because a similar 

 immunity cannot be produced in the adult animal by feeding it upon 



