CLEA VA GE THEOR Y OF PROTEID DIGESTION. 405 



with acid alone, but incomparably more slowly. The acid and ferment 

 seem to mutually assist each other. Pepsin alone is inactive, the acid 

 alone acts with extreme slowness, but in the presence of the acid the 

 ferment speedily dissolves the proteid, which is then rapidly attacked by 

 the acid and converted into acid albumin. 



When the proteid undergoing digestion is fresh fibrin which has not been 

 previously subjected to heat coagulation, a body possessing the properties of 

 a globulin is found in the solution in the first stage of digestion, before or 

 just when complete solution has taken place ; a similar body is also said to be 

 formed in small quantity as a first product of digestion of other forms of 

 proteid. 1 In a recent paper it is stated by Arthus and Huber 2 that this 

 globulin is simply dissolved fibrin. These authors found such a body co- 

 agulating at 56 C. on digesting unboiled fibrin ; but boiled fibrin yielded no 

 such product. They also determined that " Witte's Peptone " dissolved un- 

 boiled fibrin, at 40 C., giving a solution which coagulated on heating at 

 56, 68, and 75 C. 



The acid albumin is next attacked by the pepsin and further 

 altered, giving rise to a number of substances called albumoses, proteases, 

 or propeptones, and these in turn are slowly and incompletely con- 

 verted into peptones. Here the action of pepsin ceases. 



Cleavage theory of proteid digestion. The cleavage theory of 

 proteid digestion was first enunciated by Klihne in 1877. 3 He describes 

 the digestion of albumins by trypsin as taking place in two stages : in 

 the first stage the albumin is changed into peptone (amphopeptone) ; 

 in the second stage, one-half of this peptone (hemipeptone) is further 

 changed, while the other half (antipeptone) remains unaltered. Peptic 

 digestion is not essentially different from the first stage of tryptic, and 

 while it is not possible to obtain two bodies from pepsin peptone, still it 

 is probable that this substance is a mixture of two bodies, antipeptone 

 and hemipeptone, as is also the case after the first stage of tryptic 

 digestion. 



Unable to isolate two bodies from the end products of peptic 

 digestion, one of which should remain unchanged when subjected to 

 tryptic digestion, while the other broke up under like treatment into 

 leucine and tyrosine, Kiihne surmised that the cleavage might take 

 place earlier in the process of peptic digestion, and that more success 

 might attend an attempt to separate the precursors of anti- and hemi- 

 peptone, namely, the corresponding albumoses, by interrupting peptic 

 digestion at an early stage, and experimenting upon the products then 

 in solution. By interrupting peptic digestion at an early stage, two 

 substances were obtained : one was a neutralisation precipitate, which, on 

 tryptic digestion, afterwards yielded only antipeptone, and was hence 

 named antialbumose ; the other, obtained from the filtrate, was de- 

 composed by trypsin, with formation of leucine and tryosine, and was 

 hence named hemialbumose.* Kiihne 5 also reinvestigated the action of 

 acids, renaming Schiitzenberger's hemiprotein anticdbumid, and a body 



1 Brticke, Sitzungsb. d. k. Akad. d. Wissensch., Wien, 1859, Bd. xxxvii. S. 182 ; Otto, 

 Ztschr. f. physiol. Chem., Strassburg, 1883, Bd. viii. S. 129; Hasebroek, ibid., 1887, Bd. 

 xi. S. 348 ; A. Herrmann, ibid., 1887, Bd. xi. S. 508 ; Neumeister, Ztschr. /. iol., 

 Munchen, 1890, Bd. xxvii. S. 310. 



2 Arch, de physiol. norm, ct path., Paris, 1893, tome xxv. p. 447. 



3 Vcrhandl. d, naturh.-med. Ver. zu Heidelberg, 1877, K F., Bd. i. S. 236. 



4 Vide infra. 5 Loc. cit. 



