1390 



PHYSIOLOGY 



constituent of the medullary sheaths of the nerve fibres. There is a 

 corresponding proportionality between the lecithin content of milk and 

 the relative brain weight of the young animal. Thus, in the calf the 

 brain is only gi^ of the whole animal. In cow's milk lecithin is 

 present in the proportion of 14 per cent, of the total protein. In 

 the puppy the brain is ^ of the whole body and the proportion of 

 lecithin to protein in the milk is 2-11 per cent. In the infant, the 

 brain forms -! of the body weight, while the lecithin is 3-05 per cent, 

 of the protein of human milk. 



We thus see that under normal conditions the young animal is 

 supplied through its natural food with all the food- stuffs in the pro- 

 portions which it requires for its normal nourishment and growth. 

 It is impossible therefore satisfactorily to replace the natural milk 

 of an animal by that of another species. In civilised communities 

 it is becoming more and more the custom to endeavour to feed the 

 child with cow's milk, more or less modified, in the vain endeavour to 

 reproduce the properties of human milk. Among all classes this 

 involves the administering of a milk differing in its qualities and in the 

 relative proportions of its proteins, its fats, carbohydrates, and salts, 

 from human milk. So-called ' humanised ' milk is only a rough imita- 

 tion of the natural mother's milk. Among the poorer classes this arti- 

 ficial feeding means the replacement of a natural sterile food, throwing 

 very little work on the digestive organs of the child, with a foreign milk, 

 very difficult 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 there- 

 fore important to know what are the main differences 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 : 



