C 7. EAVA GE THEOR Y OF PROTEID DIGESTION. 4 1 5 
body has a powerful digestive action on proteida in fluids of cither 
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, hut 
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. 
Kiihne 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 tins 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. Kiihne 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 winch is undergoing digestion. This effect is most easily ol iserved 
if fibrin is the proteid undergoing digestion, when the coagulable proteid 
present in the solution, just before the fibrin is completely dissolved, has 
1 Ztschr.f. rat. Med., 1859, Dritte Eeihe, Bd. vii. S. 1. 
2 Virchows Archiv, 1862, Bd. xxv. S. 279. 
3 Ibid., 1867, Bd. xxxix. S. 130. 
* Verhamdl. d. I. Ver. :u Heidelberg, 1877, X. F., Bd. i. S. 233. 
5 See Neumeister, "Lehrbuch der physiologischen Chemie," Jena, 1893, S. 198; 
K. Mann, "Ueber die Absorption der proteolytischen Enzvme durch die Eiweisskbrper," 
Diss., Wiirzburg, 1892, S. 23. 
