222 



RUTH WHEELER 



180 



120 



20 40 60 80 100 120 



Days 



Chart 6 From Osborne and Mendel, Carnegie Institution of Washington, 

 Publication 156, Part II, p. 95, 1911, showing the growth of rats on milk food. 



mammals; the more rapid the growth, the greater is the protein- 

 and ash-content of the milk. This is, however, not necessarily 

 the whole secret; for when attempts were made to imitate with 

 isolated food substances the milk food found most satisfactory 

 for mice, the mice did not grow. It is of course possible that 

 this is due to the presence in milk of some special substance that 

 makes it so wonderfully adapted to its purpose; but it is also 

 possible that the physical characteristics of the casein food rather 

 than the absence from it of some e&sential constituent account 

 for the result. 21 Further work will be necessary to settle this 

 point. 



" More recent investigation by the author in the Department of Household 

 Science of the University of Illinois indicates that the trouble was due partly to 

 the physical character of the food, partly to too high calorific value. 



