64 PHYSIOLOGICAL CHEMISTRY. 



stances, of a protein nature, into the ammo acids of known chemi- 

 cal structure. In this decomposition the protein molecule is not 

 broken down in a regular manner into */, J4, y& portions and 

 the ammo acids formed in a group at the termination of the hy- 

 drolysis. On the contrary, certain amino acids are formed very 

 early in the process, in fact while the main hydrolytic action has 

 proceeded no further than the proteose stage. Gradually the com- 

 plexity of the protein portion undergoing decomposition is sim- 

 plified by the splitting off of the amino acids and finally it is so far 

 decomposed through previous cleavages that it yields only amino 

 acids at the succeeding cleavage. In short the general plan of the 

 hydrolysis of the protein molecule is similar to the hydrolysis of 

 starch. In the case of starch there is formed a series of dextrins of 

 gradually decreasing complexity and coincidently with the formation 

 of each dextrin a small amount of sugar is split off and finally 

 nothing but sugar remains. In the case of protein hydrolysis there 

 is a series of proteins of gradually decreasing complexity produced 

 and coincidently with the formation of each new protein substance 

 amino acids are split off and finally the sole products remaining 

 are amino acids. 



Inasmuch as diversity in the method of decomposing a given 

 protein does not result in an equally diversified line of decomposition 

 products, but, on the other hand, yields products which are quite 

 comparable in character, it may be argued that there are probably 

 well defined lines of cleavage in the individual protein molecule 

 and that no matter what the force brought to bear to tear such a 

 molecule apart, the disintegration, when it comes, will yield in 

 every case, certain definite fragments. These fragments may be 

 called the " building stones " of the protein molecule, a term used 

 by some of the German investigators. Take, for example, the 

 decomposition of protein which may be brought about through 

 the action of the enzyme trypsin of the pancreatic juice. When 

 this enzyme is allowed to act upon a given protein, the latter is 

 disintegrated in a series of definite cleavages, resulting in the for- 

 mation of proteoses, peptones and peptides in regular order, the 

 peptides being the last of the decomposition products which possess 

 protein characteristics. They are all built up from amino acids and 

 are therefore closely related to these acids on the one side ^nd to 

 peptones on the other. We have di-, tri-, tetra-, penta-, decZ, u..d 

 poly-peptides which are named according to the number of amino 

 acids included in the peptide molecule. Following the peptides 



