CLEAVAGE THEORY OF PROTEID DIGESTION. 415 



body has a powerful digestive action on proteids in fluids of either 

 alkaline, acid or neutral reaction. In addition, he showed that infusions 

 of the fresh gland possess a similar action, that the active material 

 is precipitated by excess of alcohol and is dissolved again on the 

 addition of water to the precipitate, and that the activity of extracts 

 of the gland depends on the time after a meal at which the animal 

 is killed, being most active when a gland is extracted that has been 

 obtained from an animal killed six to nine hours after a full meal. 

 Corvisart also showed that the proteids are not merely dissolved, but 

 converted into substances possessing the same general characters as 

 those formed in peptic digestion. 



These important results were denied at first by some observers, who 

 failed for some reason to obtain them on repeating Corvisart's experi- 

 ments, but were in the end abundantly confirmed by the researches of 

 Meissner, 1 Danilewsky, 2 and Kiihne, 3 and are now universally accepted. 



Klihne 4 not only confirmed the results of Corvisart, but made an 

 important advance, by showing that pancreatic juice owes its action to 

 an enzyme, to which he gave the name of trypsin. He next showed 

 that, although trypsin is precipitated by excess of salicylic acid, smaller 

 quantities of that substance do not stop the action of the enzyme, 

 while they do, as shown by Kolbe, stop the growth of organisms, 

 especially those concerned in putrefaction. Until this was ascertained, 

 digestion experiments with pancreatic juice were complicated by the 

 putrefactive changes by which digestion was accompanied, for, while 

 trypsin acts in a neutral, and even in a faintly acid medium, its action 

 is stopped and the ferment gradually destroyed in a medium sufficiently 

 acid to stop the growth of bacteria by virtue of its acidity alone, so that 

 no one had been able to carry out prolonged experiments on pancreatic 

 digestion without the accompaniment of putrefaction. For this reason 

 it was unknown whether certain substances which appear towards the 

 end of the digestion were really due to the action of the enzyme or 

 were products of the putrefaction. Klihne was the first to carry out 

 antiseptic digestion, and to show that these substances are really formed 

 by the agency of the trypsin; he also perfected a method of freeing 

 solutions of the enzyme from the products of proteid digestion, resulting 

 either from the self-digestion of the gland in the preparation of the 

 extracts or otherwise, thus clearing the way for a study of the various 

 products formed by the action of trypsin on proteids. 



Instead of preparing a purified solution of trypsin, which is a 

 rather troublesome process, the power possessed by fibrin of absorbing 

 the ferment, as described in the case of peptic digestion, may be 

 utilised here also ; but if the digestion of coagulated proteids is to be 

 observed, a purified solution of trypsin must be first prepared. 5 



The first action of trypsin seems to be a simple solution of the 

 proteid which is undergoing digestion. This effect is most easily observed 

 if fibrin is the proteid undergoing digestion, when the coagulable proteid 

 present in the solution, just before the fibrin is completely dissolved, has 



1 Ztsclir.f. rat. Med., 1859, Dritte Reihe, Bd. vii. S. 1. 



2 Virchow's Archiv, 1862, Bd. xxv. S. 279. 



3 Ibid., 1867, Bd. xxxix. S. 130. 



4 Verhandl. d. naturh.-med. Ver. zu Heidelberg, 1877, N. F., Bd. i. S. 233. 



5 See Neumeister, " Lehrbuch der physiologischen Chemie," Jena, 1893, S. 198; 

 K. Mann, "Ueber die Absorption der proteolytischen Enzyme durch die Eiweisskorper," 

 Diss., Wiirzburg, 1892, S. 23. 



