CHEMICAL BASIS OF THE ANIMAL BODY. 61 



Traces of pepsin and other enzymes are frequently found in urine ; 

 the literature of the subject up to the present date is fully quoted in the 

 papers to which a reference is here given *. 



Trypsin. 



The proteolytic enzyme of pancreatic juice. This appears to have 

 been first separated from the other enzymes which exist in pancreatic 

 juice by Danilewski 2 . More recently Kuhne has prepared it in quantity 

 and in what must be presumed to be a pure (?) form, by an elaborate 

 and lengthy process for the details of which his original work 

 must be consulted 3 . The composition of the enzyme as prepared by 

 Kiihne was found to be remarkably complex, as shown by the fact that 

 when dissolved in water and boiled it is split up with the formation of 

 20 p.c. coagulated proteid and 80 p.c. albumose. It might at first sight 

 appear probable from this that the purified enzyme was in reality a 

 mixture of the true enzyme with other substances (proteid) to whose 

 decomposition on boiling the coagulated proteid and albumose were due, 

 and some authors have taken this view 4 . This seems however to be 

 negatived by the fact that Kuhne digested his trypsin for several weeks 

 in dilute alkaline solution and did not observe the formation of the least 

 trace of peptone, leuciii or tyrosin. The percentage composition of the 

 enzyme has been quoted on p. 54, from which it appears to contain 

 distinctly less carbon than a true proteid. 



Preparation of solutions of trypsin for digestion experiments. The 

 following method due to Kuhne yields an extraordinarily pure and 

 active tryptic solution ; unfortunately it is a somewhat lengthy 

 process 5 . 



One part by weight of pancreas which has been extracted with alcohol and ether 

 is digested at 40 for 4 hours with 5 parts of ! p.c. salicylic acid. The residue after 

 being squeezed out is further digested for 12 hours with 5 parts of -25 p.c. Na 2 C0 3 . 

 and the residue is again squeezed out. The acid and alkaline extracts are now 

 mixed together, the whole made up to '25 '5 p.c. Na 2 C0 3 , and digested for at least 

 a week in presence of *5 p.c. thymol. By this means all the first formed albumoses 

 are fully converted into peptones ; this is essential. At the end of the week the fluid 

 is allowed to stand in the cold for 24 hours, filtered, faintly acidulated with acetic 

 acid and saturated with neutral ammonium sulphate. By this means all the trypsin 

 is separated out and may be collected on a filter where it is washed with the 



1 Stadelmann, Zt. f. BioL Bd. xxiv. (1888), S. 226. See also Wasilewski 

 (Eussian). Abst. in Maly's Bericht. 1887, S. 193. Hoffmann, Pfliiger's Arch. Bd. 

 XLI. (1887), S. 148. Helwes, Ibid. Bd. XLIII. (1888), S. 384. 



2 Virchow's Arch. Bd. xxv. (1862), S. 279. 



3 Verhandl d. naturhist.-med. Ver. Heidelbg. (N.F.), Bd. i. (1876), S. 194. 



4 Low, Pfliiger's Arch. Bd. xxvu. (1882), S. 209. 



5 Verhand. d. naturhist.-med. Ver. Heidelbg. (N.F.), Bd. in. (1886), S. 463. Also 

 Centralb. f. d. med. Wiss. 1886, Nr. 45. 



