CHEMISTRY OF DIGESTION AND NUTRITION. 301 



Several partial analyses have been reported. According to Zawadsky, 1 the 

 composition of the secretion in a young woman was as follows : 



In 1000 parts. 



Water 864.05 



Organic substances 132.51 



Proteids 92.05 



Salts 3.44 



The organic substances held in the secretion are in part of an albuminous 

 nature, since they coagulate upon heating, but the exact nature of the proteid 

 or proteids has not been determined satisfactorily. The most important of the 

 organic substances — the essential constituents, indeed, of the whole secretion — 

 are three enzymes acting respectively upon the proteids, the carbohydrates, 

 and the fats. The proteolytic enzyme is called "trypsin;" the amvlolvtic 

 enzyme is described under different names : " amylopsin " is perhaps the best, 

 and will be adopted in this section ; for the fat-splitting enzyme we shall use 

 the term "steapsin." Owing to the presence of these enzymes the pancreatic 

 secretion is capable of exerting a digestive action upon each of the three im- 

 portant classes of food-stuffs. It is said that the pancreatic juice contains 

 also a coagulating enzyme, similar to rennin, capable of curdling milk. 



Trypsin. — Trypsin is a more powerful proteolytic enzyme than pepsin. 

 Unlike the latter, trypsin acts best in alkaline media, but it is effective also in 

 neutral liquids, or even in solutions not too strongly acid. Trypsin is affected 

 by changes in temperature like the other enzymes, its action being retarded 

 by cooling and hastened by warming. There is, however, a temperature, 

 that may be called the optimum temperature, at which the trypsin acts most 

 powerfully ; if, however, the temperature is raised to as much as 70° to 80° C, 

 the enzyme is destroyed entirely. Trypsin has never been isolated in a condi- 

 tion sufficiently pure for analysis, so that its chemical composition is unknown. 

 Extracts containing trypsin can be made from the gland very easily and by 

 a variety of methods. The usual laboratory method is to mince the gland and 

 to cover it with glycerin for some time. Iu using this and other methods for 

 preparing trypsin extracts it is best not to take the perfectly fresh gland, but 

 to keep it for a number of hours before using. The reason for this is that the 

 enzyme exists in the fresh gland in a preparatory stage, a zymogen (see sec- 

 tion on Secretion), which in this case is called " trypsinogen." Upon standing, 

 the latter is slowly converted to trypsin — a process that may be hastened by 

 the action of dilute acids and by other means. An artificial pancreatic juice 

 is prepared usually by adding a small quantity of the pancreatic extract to an 

 alkaline liquid; the liquid usually employed is a solution of sodium carbonate 

 of from 0.2 to 0.5 per cent. To prevent putrefactive changes, which come on 

 with such readiness in pancreatic digestions, a lew drops of an alcoholic solution 

 of thymol may be added. A mixture of this kind, if kept at the proper 

 temperature, digests proteids very rapidly, and most of our knowledge of 

 the action of trypsin has been obtained from a study of the products of such 

 digestions. 



1 Centralblattjur Physiologie, 1891, Bd. v. S. 179. 



