THE PANCREA TIC ENZYMES. 337 



5. A very active proteolytic extract may be obtained by extracting with 

 water containing O'Ol to O05 per cent, of ammonia. The filtered extract gives 

 a precipitate with acetic acid which digests proteid very energetically, and can 

 be further purified. 1 



In preparing pancreatic extracts, it should be remembered that the 

 gland does not at all periods contain the same amount of the ferments, 

 or rather their zymogens, but that the amount fluctuates within wide 

 limits according to the period after a meal. The pancreas of an animal 

 in which digestion is not going on will yield little or no ferments ; the 

 best time is from four to seven hours after a meal. An inactive prepara- 

 tion may often be cured by making the extract faintly acid with acetic 

 acid some time before using ; this sets free ferment which may be present 

 as zymogen in the extract. 



Trypsin. 2 The proteolytic enzyme of the pancreatic juice in the 

 purest form in which Kiihne obtained it, gave all the proteid reactions, 

 thus differing from all the other purer forms of enzyme hitherto described. 

 Kiihne's product is decomposed on boiling, yielding 20 per cent, of 

 albumin and 80 per cent, of peptone ; it is soluble in water, but insoluble 

 in anhydrous alcohol or glycerin. The insolubility of the purified dry 

 product in anhydrous glycerin accords with v. Wittich's 3 observations, 

 that both enzymes can be extracted from the fresh gland by glycerin ; 

 but if the gland mass be previously thoroughly dried by extraction with 

 alcohol, glycerin only takes out the diastatic enzyme, the proteolytic 

 one being left behind. 



Influence of temperature. The activity of trypsin increases, accord- 

 ing to Eoberts, 4 with rising temperature until 60 C. is reached, and 

 then rapidly falls, all action ceasing between 75 C. and 80 C. ; 

 Biernacki 5 states that purified trypsin in 0'25 to 0*5 per cent, sodium 

 carbonate solution is destroyed in five minutes by a temperature of 

 50 C., and in neutral solution by a temperature of 45 C. The presence 

 of albumoses or of certain ammonium salts protects against the action 

 of elevated temperature in alkaline solution. 



Influence of reaction. Kiihne 6 made the observation that the activity 

 of trypsin was permanently destroyed by digesting its solutions with 

 pepjsin and hydrochloric acid, and attributed the greater share in this 

 action to the pepsin. Boas 7 afterwards showed that the destruction 

 might be due to acid action alone, by demonstrating that addition of 

 hydrochloric acid to the filtered intestinal contents causes a precipitate 

 containing nearly all the ferments. This precipitate, on standing for a 

 few hours under the acid, became inert, but, when quickly separated and 

 redissolved in sodium carbonate, showed both diastatic and proteolytic 

 action. The matter has recently been again tested by Melzer, 8 who 



1 Hammarsten, " Lehrbuch, " Wiesbaden, 1895, Aufl. 3, S. 265. 



2 So named by Kiihne, Verhandl. d. naturh.-med. Ver. zu Heidelberg, 1876, N. F., 

 Bd. i. S. 190. Danilewski (Virchoiv's Archiv, 1862, Bd. xxv. S. 279) had previously to this 

 obtained a product which failed to give many of the usual proteid reactions. 



3 Arch. f. d. ges. Physiol., Bonn, 1869, Bd. ii. S. 198 ; Hiifner (Jahresb. ii. d. Fortschr. 

 d. Thier-Chem., Wiesbaden, 1872, Bd. ii. S. 360) failed to obtain a similar result, probably 

 through using glycerin containing water. 



4 Proc. Roy. Soc. London, 1881, vol. xxxii. p. 158. 



5 Ztschr.f. BioL, Miinchen, 1891, Bd. xxviii. S. 51. 



6 Verhandl. d. naturh.-med. Ver. zu Heidelberg, 1876, N. F., Bd. i. S. 193. 



7 Ztschr.f. klin. Med., Berlin, 1890, Bd. xvii. S. 170. 



8 Inaug. Diss., Erlangen, 1894 ; Melzer's figures show that most of the destruction is due 

 to acid alone. 



VOL. I. 22 



