10 3Iendel and Underhill — Fajmin-digestion. 



obtained in the acid digestions ; and frequently t3'pical leucin crys- 

 tals, less often characteristic tyrosin crystals, could be detected with 

 the microscope. There was no difference in the three papain prepara- 

 tions in this respect. The susj^icion that the meat thus prepared long- 

 after the death of the animal might be contaminated with bacterial 

 enzymes, led to the use of dog's and rabbit's muscle removed from the 

 freshly killed animal immediately after perfusion of the blood-vessels 

 with isotonic sodium chloride solution to wash out the blood com- 

 pletely. Precisely similar results were obtained with such material 

 in the acid and neutral media. Finally trials were made with muscle 

 tissue previously heated in boiling Avater. With the boiled muscle 

 no leucin, tyrosin or tryptophan was ever obtained. These facts 

 seem to indicate the existence of an enzyme in the muscle tissue 

 which may assist in the proteolysis accomplished by papain on the 

 fresh tissue and may carry the action to a stage where relatively simple 

 products are formed. The self-digestion (autolysis) of muscle after 

 exclusion of bacteria by the use of chloroform-water, Avas observed 

 long ago by Salkowski,' He failed to find leucin and tyrosin among 

 the products. More recently Jacoby" obtained large quantities of 

 leucin, tyrosin and also tryptophan in the self-digestion of the liver. 

 These observations indicate an explanation for the exceptional results 

 obtained with fresh muscle tissue in our papain digestions, by refer- 

 ring to the muscle itself the active agent in the production of trypto- 

 phan, etc., in these cases — a conclusion which is supported by the 

 uniformly negative results obtained with the heated tissue. 



III. The JVature of some Products of PapcCin Proteolysis. 



While the experiments just outlined indicate the marked difference 

 between trypsin-and papain-proteolysis so far as the end-products 

 formed under ordinary conditions are concerned, a closer study 

 of the primary products has shown them to resemble in many respects 

 the bodies obtained under similar conditions in pepsin-hydrochloric 

 acid digestion. Our investigation in this direction has been confined 

 to the proteid casein, since this is readdy obtained in large quantities 

 in a state of considerable purity. The products formed from casein by 

 pepsin-hydrochloric acid have been investigated by Chittenden' and 



1 Salkowski : Arehiv f iir Physiologie, 1890, p. 554 ; Zeitschrift f iir klinische 

 Medicin, 1890, xvii, Supplementband, p. 77. 



= Jacoby : Zeitschrift fiir pliysiologische Chemie, 1900, xxx, p. 162. 



3 Chittenden: Studies from the laboratory of physiological chemistry, Yale 

 University, 1887, ii, p. 156; 1889, iii, p. 66. 



