138 THE DIGESTIVE FLUIDS. 



amount of thymol sufficient to saturate the solution, so as to guard 

 against putrefactive processes. The mixture is kept at a tempera- 

 ture of 40 C. If the fibrin is then dissolved and leucin or tyrosin 

 can be demonstrated in the resulting solution, the presence of trvpsin 

 may be inferred. To this end, it is only necessary to evaporate ihc 

 solution to a thick syrup and to examine this microscopically (see 

 page 188). Should the solution to be tested contain a free mineral 

 acid, or larger amounts of organic acids, no result will, of course, be 

 obtained, as the trypsin has then been destroyed. 



Isolation of Trypsin. Unless it is desired* to obtain trypsin in as 

 pure a form as possible, alkaline solutions of the common pancreatin 

 preparations which are sold in the shops can be used for experimental 

 purposes. Otherwise the method of Kiihne, as modified by Gautier, 

 should be employed : The fresh pancreas is finely hashed and 

 washed with ice-cold water, to which 1 pro mille of salicylic acid 

 has been added. After four hours the mass is treated with a 

 large amount of a 5 pro mille solution of sodium carbonate, 

 containing an excess of thymol, and is kept for twelve hours at a 

 temperature of from 37 to 40 C. The acid and alkaline extracts 

 are then mixed, treated with 0.5 per cent, of sodium carbonate, 

 filtered, feebly acidulated with acetic acid, and saturated with 

 ammonium sulphate in substance. The precipitate which then 

 separates out contains all the trypsin. It is dissolved in water, 

 filtered, and dialyzed, so as to remove the salt which is still present, 

 as also traces of peptones and leucin. The resulting solution is 

 concentrated at a very low temperature, and the trypsin finally pre- 

 cipitated with strong alcohol. It is then rapidly filtered off and 

 dried. The amount of material which can thus be obtained from 

 one gland is always very small, but sufficient to digest a large 

 quantity of albumin when dissolved in about 100 c.c. of water. 



The so-called dry pancreas of Kiihne, from which trypsin can 

 likewise be obtained, and which is also used in digestive experiments 

 as such, is prepared by extracting the fresh gland with alcohol and 

 subsequently with ether until it is free from fats. The remaining 

 material, which contains the active ferment, is then dried and pul- 

 verized, and can be kept in this form indefinitely. 



The Amylolytic Ferment of the Pancreatic Juice (Amylop- 

 sin). The amylolytic ferment of the pancreatic juice is by many 

 thought to be identical with the ptyalin of the saliva. It can be 

 isolated, according to Gautier's method, from an aqueous infusion of 

 the fresh gland that has remained exposed to the air for about 

 twenty-four hours, as already described. To demonstrate its action, 

 a few cubic centimeters of such an infusion, or a glycerin extract of 

 the gland, are added to a small amount of starch paste and kept at a 

 temperature of 40 C. The mixture is then tested for the presence 

 of maltose, as already described. 



Steapsin. It has long been known that the pancreatic juice pos- 

 sesses the power of emulsifying fats, and of decomposing these into 



