242 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



ties of these and the other products are described in the Chemical section. 

 Leucin and tyrosin have been found in the contents of the intestines, and it is 

 probable, therefore, that the splitting of the hemi-peptoue which takes place so 

 readily in artificial tryptic digestions occurs also, to some extent at least, within 

 the body, although we have no accurate estimates of the amount of peptone 

 destroyed in this way under normal conditions. On the supposition that the 

 production of leucin, tyrosin, and the other amido- bodies is a normal result of 

 tryptic digestion within the body, it is interesting to inquire what physiological 

 value, if any, is to be attributed to these substances. At first sight the forma- 

 tion of these amido- bodies from the valuable peptone would seem to be a 

 waste. Peptone we know may be absorbed into the blood, and may then be 

 used to form or repair proteid tissue, or to furnish energy to the body upon 

 oxidation, but leucin and tyrosin and the other products of the breaking up 

 of the hemi-peptone are 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 

 hemi-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 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 amido- bodies found in the aliment- 

 ary 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 theoretical importance of the base lysatinin will be referred 

 to again later, when speaking of the origin of urea in the body. The processes 

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

 schema, taken from Neumeister : l 



Proteid. 



Deutero-albumoses. 

 Ampho-peptone. 



Anti-peptone. Hemi-peptone. 



Leucin. Tyrosin. Aspartic acid. Tryptophan, etc. 



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 



1 Lehrbuch der physiologischen Chemie, 1893, p. 200. 



