4o 4 CHEMISTR Y OF THE DIGESTIVE PROCESSES. 
Meissner's views as to the decomposition of proteids on digestion 
did not at first obtain much credence. The formation of a substance 
precipitated by neutralisation, and incapable of further conversion ly 
pepsin and an arid in the course of normal digestion, was denied, and 
with right, by Briicke and others. 
Briicke 1 stated that there was no such decomposition of the pro- 
teid molecule as Meissner indicated, but that fibrin is first dissolved 
and afterwards converted in great part into acid albumin, accom- 
panied even at first by peptone in small quantity. If neutralisation 
takes place at this stage, a heavy precipitation is the result, and there 
remains in solution a small quantity of coagulable proteid (formed by 
the solution of the fibrin and not yet converted into acid albumin by 
the acid) mixed with albumoses and peptone. If, however, peptic 
digestion be allowed to proceed to completion, no precipitation occurs 
on neutralising, and the solution contains only albumoses and peptones. 
This shows that Meissner's parapeptone, as well as Kuhne's antialbumate 
and antialbumid, which will be described later, 2 are not formed to any 
extent in active peptic digestion, but are merely products of prolonged 
action of dilute acid. 
In order to study the products formed in peptic digestion, it is necessary 
to proceed with a digestive fluid which has been purified from products of 
digestion, due to self-digestion or otherwise, by one of the methods already 
described, 3 or else to take advantage of a peculiar property possessed by 
fibrin, and in a lesser degree by some other forms of proteid, of absorbing 
pepsin from solution. 4 
Any digestive fluid containing pepsin (such as that obtained h} T auto- 
digestion of pig's gastric mucous membrane in dilute hydrochloric acid) is 
carefully neutralised, using powdered chalk for the purpose, so as to avoid all 
danger of alkalinity, by which the pepsin would he rapidly destroyed. 5 After 
neutralising and filtering, the fluid is shaken up with flakes of fibrin for 
some time ; this is best done by blowing a stream of air through the mixture, 
placed in a tall vessel, by means of a Bunsen filter pump. In about an hour 
the fibrin becomes impregnated with pepsin, which, however, cannot attack it 
in the neutral fluid. So firmly adherent is the enzyme to the fibrin, that the 
latter may be freely washed without parting from it. If this fibrin be now 
placed in dilute hydrochloric acid ( - 2 per cent.) at 40° C, it is quickly dis- 
solved and digested. Instead of neutralising the impure digestive fluid, it 
may be saturated with sodium chloride, which stops the digestive action of the 
pepsin ; on now agitating thoroughly for about an hour, the fibrin is saturated 
with pepsin, after which it may be washed as before. This peculiar power of 
absorbing pepsin is shown in a varying degree by all solid forms of proteid. 
Fibrin possesses it most markedly, muscle fibre and casein also show it well, 
but coagulated proteids show it comparatively much more feebly. 6 
Fibrin, or other solid proteid, on digestion, swells up, dissolves, and 
is converted into syntonin or acid albumin. The same result is obtained 
1 Sitzungsb. d. k. Alcad. d. TPissensch., Wien, 1859, Bd. xxxvii. S. 131 ; 1861, Bd. xliii. 
S. 601. 
2 See pp. 406-409. 3 See p. 402. 
4 Von Wittich, Arch. f. d. gcs. Physiol., Bonn, 1872, Bd. v. S. 443 ; K. Mann, " Ueber 
die Absorption iter proteorytischen Enzyme duvcli die Eiweisskuriier, - ' Inaug. Diss., 
Wiirzburg, 1892, S. 23. 
5 Langley, Journ. Physiol., Cambridge and London, 1882, vol. iii. p. 253. 
6 Wurtz, Compt. rend. Acad. d. sc, Paris, ISSi, tome xeiii. p. 1104; A. Fick, 
Sitzungsb. d. phys.-med. Gesclhch. zu Wiirzburg, 1889, S. 23; K. Mann, Inaug. Diss., 
Wiirzburg, 1892. 
