CHAPTER VI 



NITROGENOUS COMPOUNDS 



(Proteins or Albuminoids] 



Occurrence. The class of proteins or albuminoids includes a 

 large number of compounds. Some of them are so much 

 alike in composition and properties that it is difficult to sepa- 

 rate them from each other, or to determine whether they are 

 one or several substances. Others differ so widely from the 

 typical compound as to give rise to difference of opinion 

 whether they should or should not be included in the 

 group. 



They are widely distributed in nature, and are of the 

 highest importance from the point of view of animal nutrition. 

 Apart from water, they constitute the chief mass of animal 

 bodies. They enter largely into the composition of eggs and 

 seeds, in which they form part of the embryonic nourishment. 

 They occur also, in solution, in the fluids e.g. blood, lymph, 

 cell sap of both plants and animals. Physiologically, they are 

 all closely related, and are derived from each other by com- 

 plex and obscure series of chemical changes. One new 

 compound may be formed out of several original substances, 

 and, like the celluloses, they probably undergo organic changes 

 subsequent to their chemical elaboration. 



These compounds have not yet been synthetically pre- 

 pared, and their exact molecular constitution is unknown. It 

 is certain, however, that they are all very complex, i.e. they 

 have high molecular weights, and are aggregates of many dif- 

 ferent groups of atoms. In some cases, the typical compound 



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