CHEMISTRY OF DIGESTION AND NUTRITION. 



:}03 



acids and nitrogenous bases, that come from the splitting of that part of the 

 peptone which can be acted upon by the trypsin, and which constitutes what 

 is known as hemi-peptone. It maybe remarked in passing that hemi-peptone 

 has not been isolated. Ampho-peptones containing both anti- and hemi-pep- 

 tones are formed in peptic digestion, and they may be obtained from tryptic 

 digestion if it is not allowed to go too far; anti-peptone, on the other hand, 

 may be obtained from tryptic digestion which has been permitted to go on until 

 the hemi-peptone has been completely destroyed, but no good method is known 

 by which hemi-peptone can be isolated from solutions containing both it and 

 the anti- form. The principal products formed by the breaking up of the 

 hemi-peptone molecule under the influence of the trypsin can be formed in 

 the laboratory by processes that are known to cause hydrolytic decomposi- 

 tions. It is probable, therefore, that these substances may be looked upon as 

 products of the hydrolytic cleavage of hemi-peptone. They are of smaller 

 molecular weight and of simpler structure than the peptone molecule from 

 which they are formed. A tabular list of these bodies, modified from Gam- 

 gee, 1 is given. The list includes only those substances that have actually 

 been isolated ; it is possible that others exist : 



Final Products (other than Peptones) of the Action of Trypsin on Albuminous and Albuminoid 



Bodies. 



Of these substances, the ones longest known and most easily isolated are leucin 

 (C 6 H, 3 N0 2 ) and tyrosin (C 9 H n N0 3 ). The chemical composition and proper- 

 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 peptone that 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 simple nitrogenous 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 formation of these simpler bodies from the valuable peptone would 

 seem to be a waste. Peptone we know may be absorbed into the blood, and 

 may then be w^^\ to form or repair proteid tissue, or to furnish energy to the 

 1 A Text-book of the Physiological Chemistry of the Animal Body, 1893, vol. ii. p. 230. 



