3 2 4 CHE MIS TR Y OF THE DIGESTIVE PR O CESSES. 
Hydrochloric acid is added to the two pepsin solutions, until the acidity 
represents 1 grm. of hydrochloric acid per litre. These are then diluted in a 
series of vessels with hydrochloric acid (1 per mille) according to the foregoing 
scheme ; the figures represent volumes, say cubic centimetres. 
A corresponding series of dilutions of the second solution is also prepared, 
and in the vessels of both series a shred of fibrin x is digested for a given time. 
At the end of the time, correspondingly advanced specimens are picked out in 
the two series, especial attention being paid to the more dilute samples, which 
give the truer indications, and the comparative power of the two solutions 
easily follows. For example, if I>o. 3 in one series corresponds to No. 5 in the 
other, the latter is four times as powerful as the former ; a closer approximation 
can then evidently be obtained by a second experiment. 
Grunhagen's 2 method. — Fibrin is swollen out by placing it for some hours 
in dilute hydrochloric acid. Equal weighed portions of this swollen fibrin are 
placed in similar filters. Over each portion an equal volume, say 1 c.c, of the 
various digestive solutions to be compared are poured. Soon the fibrin begins 
to dissolve and drop from the funnels, dissolving in the dilute acid which had 
previously swollen it. From the measured amounts dropping in equal times 
from the different funnels, or by counting the rate of the drops, the compar- 
ative activities of the various solutions can be determined. This method 
evidently cannot be used for trypsin. 
Griitzner's 3 method. — Also cannot be used for trypsin, but is one of the best 
methods for pepsin. It is a colorirnetric method, and consists in measuring 
the velocity with which the solution under examination dissolves fibrin stained 
uniformly with carmine, by means of the depth of tint imparted to the solution 
by the finely divided particles of carmine, which are set free in the solution at 
a rate proportional to that of solution of the fibrin. 
The method is best carried out by comparing the depth of the tints 
produced at observed time intervals with those of a number of standard solu- 
tions of carmine. The methods employed in preparing the stained fibrin and 
these standard tints are as follows : — The fibrin is first well washed in a stream 
of running water accompanied by kneading, 4 and then placed for twenty-four 
hours in a bath of weakly ammoniacal - 25 per cent, carmine solution, 5 the 
volume of staining fluid being large compared with that of the mass of fibrin 
to be stained, and the latter being pulled into small pieces, so as to ensure 
thorough and uniform staining. After staining for twenty-four hours, the 
fibrin is removed from the staining bath and washed well in a stream of 
running water until it ceases to colour it. Before using for a digestion experi- 
ment, the coloured fibrin in small pieces is immersed in about five times its 
volume of 0*2 per cent, hydrochloric acid for thirty to sixty minutes; this 
swells it up to a clot-like mass, and it is used in this condition, pieces of 
approximately equal size being placed in equal volumes of the various digest- 
ive fluids to be compared, contained in equal-sized test tubes. 
The scale of comparison tints may be prepared by adding, in varying pro- 
portion, a glycerin solution containing one-tenth per cent, of carmine, to water 
in test tubes of equal size; thus, to 19-9 c.c. of water are added OT c.c. of 
one-tenth per cent, glycerin-carmine solution; to 19 - 8 c.c. of water, - 2 c.c. of 
the same glycerin-carmine solution ; and so on, finishing with a solution 
1 Approximately of equal size ; a slight difference lias no appreciable effect. 
2 Arch. f. d. ges. Physiol., Bonn, 1872, Bd. v. S. 203. For a method of adopting this to 
exjwiment at body temperature, see Griitzner and Ebsteiu, ibid., 1874, Bd. viii. S. 122. 
3 Ibid., 1874, Bd. viii. S. 452 ; " Neue Untersuch. ii. Bildungu. Ausscheid. des Pepsins," 
Habilitationsschrift, Breslau, 1875. 
4 It may advantageously be left in water over night to remove accompanying haemo- 
globin. 
6 Prepared by dissolving 1 grm. of carmine in a small volume of dilute ammonia and 
making up to 400 c.c. with water ; the solution should only very faintly smell of ammonia, 
and if necessary must be left exposed to the air until the odour of ammonia almost disappears. 
