GENERAL METABOLISM. 



655 



which flows shortly after birth. This contains far more protein, and is 

 called the colostrum. Human colostrum contains in 100 parts by weight 

 in grams: 



The colostrum is found in all species of mammals. With the cow the 

 relations are as follows: 100 parts by weight of milk contain 2.90 grams 

 casein, 0.50 gram albumin, 3.70 grams fat, and 4.95 grams milk-sugar. 

 One hundred parts by weight of colostrum contain 4.19 grams casein, 

 12.99 grams albumin and globulin, 3.97 grams fat, and 2.28 grams milk- 

 sugar. The exact significance of the colostrum is not known. We can 

 indeed imagine that the tissues and cells of the new-born, which now exer- 

 cise certain functions for the first time, require a considerable supply of 

 protein. 



The composition of the milk is dependent upon a number of external 

 conditions. 1 Cow's milk, especially, has been much studied as regards 

 the influence of various factors upon the composition and amount pro- 

 duced per day. One of the chief factors is the breed, and another the 

 nature of the nourishment the animal receives. Moving about and work 

 have an effect. 



The variations in the composition of the milk are not great under 

 normal conditions. This is very important. The fact that the milk of 

 different species of animals varies greatly is of much significance. The 

 composition of the milk evidently has an effect upon the rate of devel- 

 opment of the suckling. 2 It is natural to expect that the richer the milk 

 is in its organic and inorganic constituents, the more rapidly the suckling 

 is able to build up its tissues. If the milk of different species of animals 

 all had the same composition, then the desired effect could be produced 

 only by means of a much greater production of milk, and similarly a corre- 

 spondingly greater quantity would have to be taken into the system of the 

 suckling. The question arises whether the milk of one species of animals 

 can be substituted for that of another. Our experience concerning meta- 

 bolism does not show us a priori any reason why this could not be done, 

 provided of course that the suckling should receive the same amounts of 

 nutriment, both qualitatively and quantitatively. 3 It is, to be sure, con- 



* Cf. Konig: loc. cit. p. 601. 



2 Cf. Lecture XVII, p. 404. 



3 Cf. Max Rubner and Otto Heubner: Z. exper. Path. Therap. 1 (1905). Franz 

 Tangl: Pfliiger's Arch. 104, 453 (1905). Camerer: Z. Biol. 16, 24 (1880); 20, 566 (1884). 



