256 PROTEIN THERAPY 



have been synthetically prepared by linking two or more amino acids 

 di-peptids, tri-peptids, etc. They are not coagulable by heat, are 

 easily soluble and may still give a biuret reaction. 



The Amino- Acids. The amino-acids form the ultimate molecular 

 units from which the proteins are constructed. They are grouped into 

 five classes: 



1. The Aliphatic or Mono-amino, monocarboxylic acids, includ- 

 ing glycocoll, alenin, valin, etc. 



2. The Mono-amino, dicarboxylic acid group including aspartic 

 acid and glutamic acid. 



3. The Isocylic, amino-acids such as tyrosin and phenyl alanin. 



4. The Heterocylic, amino-acids including histidin, tryptophan, 

 prolin, etc. 



5. The Diamino-monocarboxylic acid group with arginin and 

 lysin. 



In general the lower split products of the proteins, including the 

 amino acids, are relatively nontoxic and bring about little or no re- 

 action on the part of the patient when injected; the compounds con- 

 taining the various ring groupings of the carbon atom as well as the 

 diamino group seem, however, to be exceptions. Considerable work 

 has recently been reported by Dale and his associates and by Koessler 

 and Hanke in connection with the toxicity of histamin. 



