8 Mendel and Underhill — Papa'in-digestlon. 



litres of 0.6 per cent. HCl at 40°-45° C. for two months. Experi- 

 ments of this type will scarcely appeal to one as offering reliable 

 evidence regarding the work of the enzyme ))epsin, especially as no 

 control experiments to show the influence of such large excesses of 

 free hydrochloric acid are presented. How vigorously dilute acids 

 alone may act on proteids has been shown by Fr. Goldschmidt.' 

 More important, however, are experiments like those of Pfaundler.^ 

 This investigator showed that while in prolonged pepsin-HCl diges- 

 tion there arise products which no longer give the biuret reaction, 

 leucin and tyrosin cannot be found ready formed. Tryptophan, in 

 particular, has always been regarded as a typical product of tryptic 

 enzymes, although Malfatti^ has recently observed that it may be 

 formed by extracts of the stomach. He gives no conclusive proof, 

 however, that the action is due to the enzyme pepsin, Tyrosin has 

 not been found among the products of pepsin-proteolysis, 



Bertrand* and others have shown that extracts of Rassida delica 

 and other species of fungi contain an oxidizing enzyme, which they 

 named tyrosinase, and which brings about a black coloration when 

 added to solutions containing tyrosin. The reaction is one of oxida- 

 tion and may be observed w4th many genera. Harlay^ has subse- 

 quently asserted that this reaction is a delicate test for the presence 

 of tyrosin and enables one to distinguish between the products of 

 peptic and tryptic digestion. With peptic digestion mixtures the 

 extracts of RksskIci yield a red, then green color; tryptic products 

 turn red, then black. Applying this test to the products of papain 

 digestion, Harla}^" has observed a resemblance in reaction to that 

 obtained with the peptic digestion products. Although these obser- 

 vations, published during the progress of our experiments, were 

 made with extracts of a different member of the papaw family, viz., 

 Carica hastifoUa, they lend additional evidence to the results which 

 we have obtained with the closely related species. 



' Goldschmidt : Ueber die Wirkung von Sanren auf Eiweissstoffe. Inaugural- 

 Dissertation, 1898, Strassbtirg. 



- Pfanndler : Zeitschrift fiir physiologische Chemie, 1900, xxx, p. 99. 



^Malfatti : Zeitschrift fiir physiologisclie Cliemie, 1900, xxxi, p. 43. 



"• Bertrand : Bulletin de la societe chimique, 1896 (3). xv, p. 793. Bourquelot : 

 Bulletin de la soei^te mycologique de Finance, 1897, xiii, p. 65. Cf. also Green : 

 The Soluble Ferments and Fermentations, 1899, pp. 299, 300. 



'" Harlay : Journal de pharmacie, 1899 [vi] 5, p. ^25. 



^ Harlay : Abstract in Journal of the Chemical Society, 1900, Part I, July, 

 p. 419. 



