PRE PAR A TION OF DIGESTIVE EXTRA CTS. 3 1 5 
ammonium sulphate by dialysis, and may be precipitated by alcohol, filtered 
off and dried as quickly as possible. 
The preparation of a purified trypsin solution is carried out by 
Ktihne's 1 method much on the same lines: — 
The pancreas first has all its fat removed by extraction with alcohol 
followed by ether, after which process it forms Kiihne's "pancreas powder." 
This is digested with five times its volume of 0*1 per cent, salicylic acid for 
about four hours. The residue is next digested with - 25 per cent, sodium 
carbonate solution for a further period of twelve hours, and the solution is 
separated from the undissolved part. The two extracts are now mixed, the 
mixture made up with carbonate of sodium solution to a strength of 0"25 to a 
- 5 per cent, carbonate, and allowed to digest at 40° C. for a week, thymol being 
added to prevent putrefaction (0 - 5 per cent.). During this time the albumoses 
become converted into peptones, and on saturating the cold solution, made 
very faintly acid with acetic acid, with ammonium sulphate, trypsin is 
precipitated, accompanied by traces only of unconverted albumoses. The pre- 
cipitate so obtained is sufficiently pure for all digestion experiments. It 
contains so little accompanying albumose, that, from 10 grms. of pancreas 
powder, merely a thin yellowish slime is obtained on the filter paper, yet this, 
when taken up by 100 c.c. of - 25 per cent, sodium carbonate solution, forms 
a strong digestive fluid. This gives an idea of the extreme power of the 
digestive ferments, and shows at the same time in what mere traces thej r 
must be present in the glands. This product may be still further purified by 
partially precipitating the solution obtained from it with excess of alcohol, 
dissolving in water, separating by dialysis the bulk of the ammonium sulphate 
also precipitated by the alcohol, removing the last traces of ammonium sulphate 
by barium carbonate, and finally precipitating as a snoAV-white amorphous 
substance by excess of alcohol. 
This pure product gives all the proteid reactions (unlike Briicke's 
pepsin), but in spite of all the elaborate and painstaking processes used 
in its preparation, there is no evidence that it does not still contain 
traces of proteid along with trypsin: the other conclusion of course 
would be that trypsin is itself a proteid. 
Preparation of digestive extracts. — "When the object is simply to 
test or demonstrate the action of the enzymes, and the admixture of 
products of digestion formed from the gland tissue is a matter of no 
moment, much simpler methods of preparation may be employed than 
those above described. 
1. In many such cases a simple extraction of the gland with water may 
be used, if the action is to be tested immediately. 
2. A general method of obtaining digestive extracts is that first recom- 
mended by v. Wittich, 2 which consists in preparing a glycerin extract. Such 
an extract has the advantage of efficiency and stability. It contains a good 
deal of proteid, and cannot be used where the products of digestion are to be 
exactly studied, but for general laboratory work glycerin extracts are most 
convenient preparations. They are easily made, and may lie preserved for 
years. As the glycerin only slowly extracts the enzymes, the same tissue will 
continue for a long time to yield fresh extracts, if fresh glycerin be added. 
A glycerin extract should not be made with a quite fresh gland, but with 
1 Untersuch. a. d. physiol. Inst. d. Univ. Heidelberg, 1878, Bd. i. S. 222 ; Verhandl. d. 
naturh.-med. Ver. zu Heidclbercj, 1886, N. F., Bd. iii. S. 463. See also ibid., 1876, N. F., 
Bd. i. S. 195. 
2 Arch. f. d. ges. Physiol., Bonn, 1869, Bd. ii. S. 193; 1870, Bd. iii. S. 339. 
