62 ENZYMES OR SOLUBLE FERMENTS. 



ammonium salt (sat. sol.) till free from peptones. It is now finally dissolved off the 

 filter in a little '25 p.c. solution of Na 2 C0 3 , to which thymol is added and thus an 

 extremely active and very pure digestive solution is obtained. Ten grams of the 

 original pancreas yield 80 100 c.c. of extract. 



Although Benger's 'liquor pancreaticus ' contains in addition to the enzymes 

 both leucin and tyrosin together with proteids, it is so actively proteolytic that the 

 small amount required to yield an active digestive solution introduces an amount of 

 impurities which may be neglected in many cases. The above impurities may be 

 largely got rid of by precipitating out the enzymes with alcohol as described on 

 p. 58. 



Although trypsin exhibits its hydrolytic powers to the greatest 

 advantage in presence of an alkali, its activity is scarcely so directly 

 related to the alkali as is that of pepsin to dilute hydrochloric acid. 

 Thus it will digest proteids although much more slowly in a neutral 

 solution and even in presence of dilute ('012 p.c.) hydrochloric acid, 

 but the slightest excess (! p.c.) of the acid destroys it 1 . In 

 connection with these statements it must however be borne in mind 

 that proteids have the power of readily combining with acids, 

 hence the addition of say ! p.c. of hydrochloric acid to a digestive 

 mixture does not imply that there is then -1 p.c. of free acid in the 

 solution 2 . 



This comparative independence of tryptic activity in its relations 

 to the reaction of the digestive mixture is doubtless of consider- 

 able physiological significance. The reaction of the contents of the 

 small intestine is very variable. The chyme as discharged from the 

 stomach is of course acid, and this acidity is largely diminished by 

 the advent of the strongly alkaline bile and pancreatic juice, so chat 

 the reaction may become alkaline within a short distance of the 

 pylorus. On the other hand the alkaline reaction may not be at 

 all appreciable until the lower end of the intestine is reached and 

 frequently, at least in dogs, the reaction is faintly acid throughout, 

 whether they are fed on proteids or on a mixture of carbohydrates and 

 fat 3 . The acidity in the latter case is not surprising bearing in mind 

 the readiness with which the carbohydrates undergo a lactic fermenta- 

 tion, especially inside the intestine, and it might therefore have been 

 abnormal in the dog whose food does not normally contain carbohy- 

 drates. On the other hand in man, living on a mixed diet, the 



1 Kiihne, Virchow's Arch. Bd. xxxix. (1867), S. 130. Heidenhain, Pfliiger's 

 Arch. Bd. x. (1875), S. 570. Mays, Untersuch. a. d. physiol. Inst. Heidelb. Bd. in. 

 (1880), S. 378. Lindberger (Swedish). See Abst. in Maly's Jahresber. Bd. xin. 

 (1883), S. 280. 



2 Szabo, Zt. f. physiol. CJiem. Bd. i. (1877), S. 140. Danilewsky, Centralb. f. d. 

 med. Wiss. 1880, No. 51. v. d. Velden, Deut&ch. Arch. f. Klin. Med. Bd. xxvu. 

 (1880), S. 186. Of. Langley and Eves, Jl. of Physiol. Vol. iv. (1882), p. 19. 



3 Schmidt-Miilheim, Arch. f. Physiol. Jahrg. 1879, S. 39. Cash, Ibid. 1880, S. 

 323. Lea, JL Physiol. Vol. ix. (1890), p. 256. 



