SUMMARY OF CHAPTER II 



ON THE GENERAL COMPOSITION OF MILK 



ALL classes of mater als which are necessary to maintain life are 

 represented in milk. The relative amounts of these vary greatly 

 in the milk of different species, and differences are also found in the 

 chemical composition of the members of different classes of food- 

 stuffs. 



Of the three main classes of food-stuffs, two protein and 

 fat are represented in milk by more than one variety of the class. 

 These constituents vary in different species, both in the percentage 

 amount present and in their chemical composition. 



In considering the chemical composition of milk with any 

 degree of accuracy, the milk of each species must be dealt with 

 separately. It is proposed here to deal only with human milk 

 and with cows' milk, since this latter milk is the most usual form 

 of food for children who are unable to obtain human milk or who 

 have been weaned. 



Proscher showed many years ago that the milk of each species 

 was adjusted so as to contain a suitable proportion of such sub- 

 stances as were needed for the young of that species. When the 

 young animal was born in a state of relative maturity, the milk 

 contained a high proportion of protein and conversely. 



It is difficult to compare the condition of the young of different 

 species at birth as regards maturity or immaturity, but the young 

 of the human species, especially compared with the calf, can safely 

 be regarded as relatively immature at birth. 



In this chapter only the proportions of the classes of food- 

 materials will be considered, and the changes in composition 

 occurring at different periods of lactation, or from other causes. 



Average Composition of Cows' Milk and of Human Milk. 

 It will be shown in the course of this chapter that there is no exact 

 standard for the composition of the milk of any species, but it 

 will be convenient to consider the average composition of a number 

 of samples. The figures given below have been obtained by various 

 investigators : 



