CHEMISTRY OF DIGESTION AND NUTRITION. 



241 



true digestive action of trypsin, but to a partial solution of the fibrin by the 

 inorganic salts in the liquid. In general, however, the preliminary stage of 

 a soluble proteid is missed, as also is that of the primary proteoses. The 

 proteid falls at once by hydrolytic cleavage into deutero-proteoses, and these 

 in turn are transformed to peptones (ampho-peptones). Just at this point 

 comes in one of the most characteristic differences between the action of pepsin 

 and that of trypsin. Pepsin cannot affect further the ampho-peptones, but 

 trypsin may act upon the supposed hemi- constituent and split it up, with the 

 formation of a number of much simpler non-proteid bodies, most of which are 

 amido-acids. The final products of prolonged tryptic digestion are, first, a pep- 

 tone which cannot further be decomposed by the enzyme and which constitutes 

 what is known as anti-peptone, and, second, a number of simpler organic sub- 

 stances, mainly amido-acids, that come from the splitting of that part of the 

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

 is known as hemi-peptone. It may be 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 simpler products formed by the breaking up of the hemi- 

 peptone molecule under the influence of the trypsin can be formed, in part at 

 least, in the laboratory by processes which are known to cause hydrolytic 

 decompositions. 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, taken from Gam- 

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

 been isolated ; it is possible that others exist : 



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



Bodies. 



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

 (C 6 H 13 NO 2 ) and tyrosin (C 9 H U NO 3 ). The chemical composition and proper- 



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

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