122 A. I. RINGER 



de novo or not. Abderhalden prepared a mixture of amino acids con- 

 sisting of the following: 



Of this mixture he gave 25 grams per day to dogs whose nitrogen, metabo- 

 lism had been studied for periods of over seventy days. In addition to the 

 amino acids, the dogs received daily 2.0 grams of predigested nucleic acids 

 from thymus and yeast, 50.0 grams of a mixture of glycerin, oleic, stearic 

 and palmitic acids, 20.0 grams of cholesterin, 50.0 grains of glucose, 5.0 

 grams of nitrogen-free bone ash and salts. This experiment lasted for 

 eight days, and throughout the entire period the animal was able to main- 

 tain nitrogenous equilibrium and to retain its*body weight. 



The remarkable thing about this experiment is, that the animal received 

 all of its food in its elementary form, and it had to synthesize not only its 

 own protein, but also its fat. 



This method of study is of great importance, because it enables us to 

 make any kind of desirable mixture of amino acids, and also enables 

 us to eliminate one or more amino acids and study their individual influ- 

 ences. 



Thus he found that an amino acid mixture, containing no glycocoll or 

 prolin, will enable an animal to maintain nitrogenous equilibrium. He also 

 found that he can replace arginin by ornithin and obtain nitrogenous 

 equilibrium. This proves that the body is capable of forming its own 

 glycocoll and prolin and that the arginin union can be accomplished in 

 the body. 



He also proved that animals can utilize, with equal completeness, the 

 amino acid mixtures obtained from the following digested proteins : casein, 

 ox beef, milk powder, egg albumin, horse meat and dog meat. 



Incomplete Proteins. In the early studies of protein metabolism it 

 was discovered that certain proteins could not maintain nitrogenous equilib- 



