INORGANIC FOODS. 



367 



A glance at the above table shows that the composition of milk varies 

 with different animals. The values also vary in the case of different 

 animals of the same species, but during the suckling period the variation 

 is only within narrow limits. We shall find that the amount of ash and 

 also of the inorganic material bears a certain relation to the rapidity with 

 which the tissue is formed as shown by the body weight. 



It is interesting now to trace the relations between the composition of 

 the milk (especially that of its ash) and that of the suckling. It is of 

 course obvious that such a comparison will serve to give us merely a rough 

 idea of these relations, for our present methods of analysis are not suffi- 

 ciently delicate for us to attempt to explain the way in which the differ- 

 ent elements are combined. The analysis of the ash, for example, merely 

 shows us what inorganic material is present, and gives us absolutely no 

 conception of the manner in which these elements are combined in the 

 body. We do not know from this whether the phosphoric acid that we 

 find was present entirely as calcium phosphate or other phosphates, or 

 whether it represents in part lecithin. At the same time the knowl- 

 edge of the constituents of the ash forms a basis for further investiga- 

 tion, and with the above-mentioned limitations gives us some means for 

 comparison. 



Now it is a striking fact, as the figures below will show, that milk has 

 such a different composition from the elements out of which it is formed; 

 namely, the blood, and especially the blood-serum. The cells of the milk- 

 glands must possess the power of selection. Now, what determines the 

 composition of the milk? Bunge, 1 with reference to this question, com- 

 pared the composition of milk-ash with that of the suckling itself, and 

 found in the case of dogs the following relations: 



Z. physiol. Chem. 13, 399 (1889) and Arch. Anat. Physiol. 1886, 539. 



