304 AX AMERICAN TEXT-BOOK OE PHYSIOLOGY. 



bod v upon oxidation, but leucin and tyrosin and the other products of the 

 breaking' up of peptone arc far less valuable as sources of energy, and so far 

 as we know they cannot be used to form or repair proteid tissue. But we 

 must be careful not to jump too hastily to the conclusion that the splitting 

 of the peptone is useless. It remains possible that a wider knowledge of the 

 subject may show that the process is of distinct value to the body, although it 

 must be confessed that no plausible suggestion as to its importance has yet 

 been made. In addition to any possible functional value which these amido- 

 bodies and nitrogenous bases may possess, their occurrence in proteolysis is 

 of immense interest to the physiologist. Some of them are of a constitution 

 simple enough to be studied by exact chemical methods, and the hope is 

 entertained that through them a clearer knowledge may be obtained of the 

 structure of the proteid molecule. It should be added that not only are these 

 bodies found in the alimentary canal as products of tryptic digestion, but 

 that they, or some of them, occur also in other parts of the body, especially 

 under pathological conditions, and that, furthermore, they occur among the 

 products of the destruction of the proteid molecule by laboratory methods or 

 by the action of bacterial organisms. The different stages in a complete 

 tryptic digestion as outlined above are represented in brief in the following 

 schema, modified from Neumeister: 1 



Proteid. 



I 

 Deutero-albumoses. 



Peptone. 



Anti-peptone. Hemi-peptone. 



Leucin. Tyrosin. Aspartic acid. Nitrogenous bases. 



It may be said in conclusion that trypsin produces peptone from proteids more 

 readily than does pepsin. Under normal conditions it is probable that most 

 of the proteid of the food receives its final preparation for absorption in the 

 small intestine, under the influence of this enzyme. 



Albuminoids. — Gelatin and the other albuminoids are acted upon by 

 trypsin, the products being similar in general to those formed from the pro- 

 teids. As stated on page 2!>7, pepsin carries the digestion of gelatin mainly to. 

 the gelatose stage ; trypsin, however, produces gelatin peptones. It seems 

 probable, therefore, that the final digestion of the albuminoids also is effected 

 in the small intestine. 



Amylopsin. — The enzyme of the pancreatic secretion that acts upon 

 starches is found in extracts of the gland, made according to the general 

 methods already given, and its presence may be demonstrated, of course, in 

 the secretion obtained by establishing a pancreatic fistula. The proof of the 

 existence of this enzyme is found in the fact that if some of the pancreatic 

 secretion or some of the extract of the gland is mixed with starch paste, the 

 1 Lehrbuch der physiologischen Chemie, 1S93, S. 200. 



