CHAP. II.] 



METHODS OF PREPARING PEPSIN. 



89 



period of from eight to fourteen days ; and in order to avoid putre- 

 factive changes thymol may be added to the liquid which is being 



FIG. 7. KUHNE'S ARRANGEMENT FOR DIALTSING IN A CONTINUOUS STREAM OF WATER. 



dialysed or the acid which has diffused away must from time to time 

 be restored (Hammarsten) 1 . It is obviously desirable to keep the 

 bag or tube in a state of continuous or rythmically interrupted agita- 

 tion by the aid of a motor, as in Lea's apparatus figured at Page 46. 



1 The non-diffusibility of pepsin was also shewn by Wolffhiigel in a paper entitled 

 'Ueber Pepsin und Fibrinverdauung ohne Pepsin.' Pfliiger's Archiv, Vol. vu. (1873), 

 p. 188. 



