CHEMISTRY OF DIGESTION AND NUTRITION. 239 



while that from rabbits is a thin, perfectly colorless liquid which does not form 

 a clot. In dogs the secretion from a permanent fistula soon becomes thinner 

 than it was when the fistula was first established, and this change in its con- 

 sistency is accompanied by a corresponding variation in specific gravity. The 

 specific gravity (dog) of the juice from a temporary fistula is given at 1030 ; 

 from a permanent fistula, at 1010 to 1011. The secretion coagulates upon 

 being heated, owing to the proteids held in solution, and it undergoes putre- 

 faction very quickly, so that it cannot be kept for any length of time. The 

 analysis of the secretion most frequently quoted is that given by C. Schmidt, 

 as follows : 



Pancreatic Juice (Dog). 



The composition of normal human pancreatic juice has not been determined 

 completely, owing to the rarity of opportunities of obtaining the secretion. 

 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 amylolytic 

 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. 



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 being hastened by warming. There is, however, a temperature, 

 1 Centralblattfur Physiologic, vol. 5, 1891, p. 179. 



