PRODUCTS OF TRYPTIC DIGESTION. 507 



alkali salts disturb tryptic digestion only slightly, and NaCl seems to 

 have the strongest action. The sulphates have a much stronger retard- 

 ing action than the chlorides. The nature of the proteins is also of 

 importance. Unboiled fibrin is, relatively to most other proteins, dis- 

 solved so very quickly that the digestion test with raw fibrin gives an 

 incorrect idea of the power of trypsin to dissolve coagulated protein 

 bodies in general. Boiled fibrin is digested with much greater difficulty 

 and also requires a higher alkalinity: 8 p. m. Na2COs (VERNON 1 ). 

 The resistance of certain native protein solutions, such as blood-serum 

 and egg-white, against the action of trypsin is remarkable. In regard 

 to the inhibition of the action of trypsin see Chapter I, page 63. 



The Products of the Tryptic Digestion. In the digestion of unboiled 

 fibrin a globulin which coagulates at 55-60 C. may be obtained as an 

 intermediary product (HERRMANN 2 ). Besides this, one obtains from 

 fibrin, as well as from other proteins, the products previously men- 

 tioned in Chapter II. In trypsin digestion the cleavage may proceed 

 so far that the mixture fails to give the biuret reaction. This does not 

 indicate, as E. FISCHER and ABDERHALDEN have shown, a complete 

 cleavage of the protein molecule into mono- and diamino-acids, etc. 

 In tryptic digestion, as shown by ABDERHALDEN and REINBOLD, using 

 the protein edestin, and by ABDERHALDEN and VOEGTLIN 3 with casein, 

 a gradual cleavage of the protein takes place, and thereby certain amino- 

 acids, like tyrosine and tryptophane, are readily and completely split 

 off, while others, like leucine, alanine, aspartic acid, and glutamic acid, 

 are slowly and less readily split off, and others, such as a-proline, phenyl- 

 alanine, and glycocoll, stubbornly resist the cleavage action of the trypsin. 

 The polypeptide-like bodies discovered by FISCHER and ABDERHALDEN, 

 which are produced in digestion, and which do not give the biuret 

 reaction, are the atomic complexes which resist the action of trypsin. 

 These peptoids contain the pyrrolidine carboxylic acid and phenylal- 

 anine groups of the protein, but also yield other monamino-acids such 

 as leucine, alanine, glutamic acid, and aspartic acid. Among the above- 

 mentioned products we find on the autodigestion of the gland other 

 substances, such as oxyphenylethylamine (EMERSON), which is pro- 

 duced from tyrosine by fermentive CO2 cleavage, also uracil (LEVENE), 

 guanidine (KUTSCHER and OTORI), the purine bases, which originate 

 from the nuclein bodies, and choline, which latter is formed from lecithin 



1 Journ. of Physiol., 28. 



2 Hermann, Zeitschr. /. physiol. Chem., 11. 



3 Abderhalden and Reinbold, Zeitschr. f. physiol. Chem., 44 and 46, with Voegtlin, 

 ibid. 53. 



