NUTRITION AND GROWTH 143 



results when a similar form of dietary was used. By 

 considerable variation in the non-nitrogenous portion 

 of the food Rohmann showed that mice will thrive 

 for weeks. A criticism of these experiments is that 

 the range of variation in the make-up of the dietary 

 resulted really in furnishing the animals an ordinary 

 mixed diet. The experiments of Jacob with pigeons, 

 of Falta and Noeggerath, and of Knapp with rats 

 demonstrated that variety in the dietary undoubtedly 

 tends toward prolongation of life but that death 

 eventually ensues. 



After experiencing many failures, Osborne and 

 Mendel have succeeded in maintaining white rats for 

 long periods of time upon single, pure, isolated pro- 

 teins, growth also being at a normal rate. They 

 attributed their success to the addition to the dietary 

 of what they term "protein-free milk." This is pre- 

 pared by removing the protein and fat from milk, 

 leaving the milk sugar, inorganic salts and the un- 

 known components. "Protein-free milk" always con- 

 tains very small quantities of protein but not enough 

 to support life. They have also demonstrated that 

 by artificially imitating the composition of "protein- 

 free milk" by union of the various ions fairly success- 

 ful results have been obtained. It is therefore pos- 

 sible to construct a dietary in such a manner from 

 purified isolated foodstuffs and artificial salt mixtures 

 that animals may not only be maintained but normal 

 growth may also be induced. 



In their work, Osborne and Mendel differentiate 



