4 o 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 acid in the course of normal digestion, was denied, and 

 with right, by Briicke and others. 



Briicke l 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 Kiihne'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 by 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 be 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. Jc. Akad. d. Wissensch. , Wien, 1859, Bd. xxxvii. S. 131 ; 1861, Bd. xliii. 

 S. 601. 



2 See pp. 406-409. 3 See p. 402. 



4 Von Wittich, Arch. /. d. ges. PhysioL, Bonn, 1872, Bd. v. S. 443 ; K. Mann, "TJeber 

 die Absorption der proteolytischen Enzyme durch die Eiweisskorper," Inaug. Diss., 

 Wtirzburg, 1892, S. 23. 



5 Langley, Journ. PhysioL, Cambridge and London, 1882, vol. iii. p. 253. 



6 Wurtz, Compt. rend. Acad. d. sc., Paris, 188i, tome xciii. p. 1104; A. Fick, 

 Sitzungsb. d. pTiys.-med. Gesellsch. zu Wurzburg, 1889, S. 23 ; K. Mann, Inaug. Diss., 

 Wtirzburg, 1892. 



