FEEDING EXPERIMENTS WITH MICE 



221 



TABLE 1 



III 



Milk powder 



Starch 



Lard 



Protein-free milk 

 Casein 



per cent 



60.0 



16,7 



23,3 



0,0 



0.0 



per cent 



100 

 

 

 

 



per cent 



50,0 



0,0 



7.7 



25.0 



17.3 



100.0 



100 



100.0 



growth) and the milk food represented above in column I re- 

 spectively. The close approximation of the growth curve of milk- 

 fed animals of the two species to that of the controls ('normal' 

 growth) indicates how satisfactory the milk foods were: milk 

 food I (table 1) to the rats and milk food III to the mice. Rats 

 and mice are quite comparable during the fourth week after 

 birth, since both species at this time begin to take extraneous 

 food in addition to their mother's milk. Using as a starting 

 point the weight reached by the two species respectively, twenty 

 days after birth, 2" rats double their weight in twenty days; 

 mice in about half that time. The milk food used for rats con- 

 tained 18 per cent protein and 3 per cent ash. On this mice are 

 .stunted as they are on the corresponding casein food; but with 

 the protein (in milk-food) increased to 29 per cent and the ash 

 to 6.8 per cent normal growth may take place. The smaller 

 animals, growing nearly twice as fast, apparently need a double 

 amount of bone- and flesh-forming food substances. The same 

 principle has been found to pertain in the natural milk of various 



^° See Charts xxii (p. 87) and xxin (p. 88) Osborne and Mendel : Publication 

 156, Part II, Carnegie Institution of Washington, 1911. 



