THE PROTEINS. 



The proteins are complex compounds of C, H, 0, N, and S 

 (in some cases P and Fe) occurring widely distributed in the 

 plant and animal kingdoms. The members of this class of 

 bodies, although differing greatly in chemical and physical 

 characteristics, possess in common certain definite properties 

 and chemical reactions which allow of classification and sub- 

 division. The proteins form the chief type of the food- 

 stuffs, since the nitrogen present in them is absolutely essen- 

 tial in order to sustain life. 



They may be divided as follows: 



The simple proteins, those giving upon decomposition 

 indole, skatole, tyrosine, cystine, amino acids, pyrrol deri- 

 vatives, etc. 



The conjugate proteins, composed of a simple protein and 

 a complex non-protein component. 



The derived proteins, derivatives of the proteins and 

 formed through hydrolytic changes. 



Reactions General to all Proteins. 



For the following tests make use of dried egg-white or 

 casein : 



Test the substance for carbon and hydrogen. 



Nitrogen. (a) Make an intimate mixture of the sub- 

 stance with soda-lime and place it in a dry test-tube. Warm 

 gently. Hold a piece of moistened red litmus paper or a 



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