PREPARA 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 

 Klirme'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 Kuhne'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 0'25 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 

 0'5 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 0'25 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 they 

 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 snow-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 be 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 Heidelberg, 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. 



