404 



LECTURE XVII. 



60 grams. The amount of phosphorus required in the food is naturally 

 even far greater, because in the above estimate it was not taken into con- 

 sideration that phosphorus is constantly being eliminated in the form of 

 phosphates. In one liter of human milk there is present 0.19 gram 

 phosphorus, ass's milk contains 0.76 gram, cow's milk 0.79 gram, and 

 goat's milk 0.96 gram. Human milk, therefore, is deficient in phos- 

 phorus; it contains less than any of the other kinds of milk which have 

 been analyzed. This is a remarkable fact, for we know that the human 

 offspring is able to construct, while still nursing, a nervous system which 

 is but slightly developed. Compared to human milk, that of the above 

 animals is extremely high in phosphorus. There must be some reason 

 for this difference. Bunge, who noticed this fact in his analyses of differ- 

 ent kinds of milk, compared the percentage composition of the ash with 

 the rate of development of the species. 1 It is to be assumed a priori that 

 an animal which develops rapidly will require more building material 

 than one whose development is slower. If we compare the time required 

 by the suckling to double its weight at birth with the amounts of albumin 

 and ash perhaps the most essential constituents for the formation of 

 the tissues contained in 100 parts of milk, it is evident at a glance that 

 the amount of these increases in proportion as the development of the 

 animal is rapid. This is shown by the following table: 2 



The composition of the milk of a single species is by no means constant. 

 The amount of albumin and ash diminishes with the age of the suckling. 

 This likewise has an effect upon the rate of growth as shown by the fol- 

 lowing values : 5 



1 Fr. Proscher: Z. physiol. Chem. 24, 285 (1897). 



2 Abderhalden: ibid. 27, 594 (1899). 



3 Abderhalden: Z. physiol. Chem. 26, 487 (1899). 



4 Ibid. 27, 408 (1899). 

 6 Ibid. 27, 457 (1899). 



