88 METHODS OF PREPARING PEPSIN. [BOOK II. 



paragraph. It may be noted that much less pepsin is obtained from 

 a mucous membrane which has been treated with absolute alcohol, 

 than from one which has been simply dried or taken fresh. 



Methods of Pepsin in solution appears to be absolutely indif- 

 purifying pep- fusible through parchment-paper. Given, then, an 

 sin based up- ac ^ solution such as artificial gastric juice, which 



fusiMUt n dl contains traces of albumoses, small quantities of 

 peptones and pepsin, the first-named bodies may be 

 got rid of by long-continued dialysis and filtration, a dilute 

 aqueous solution of pepsin ultimately remaining in the dialyser 1 . 

 The non-diffusibility of pepsin from a solution containing it into 

 pure water was first pointed out by v. Wittich 2 , who however stated 

 that when the dialyser was surrounded by dilute hydrochloric acid 

 (of 0*2 per cent.), pepsin did diffuse. Hammarsten 3 afterwards shewed 

 that the latter statement was incorrect, and established the fact 

 of the absolute indiffusibility of pepsin into either neutral or acid 

 solutions. 



In order to prepare a solution of pepsin by the aid of dialysis, 

 we may proceed in various ways, as (a) an artificial gastric juice, 

 made in the way previously described, is subjected to dialysis for a 

 period of several days, (b) Having followed out Briicke's method 

 for the preparation of pepsin so far as the solution of the pepsin- 

 containing precipitate of calcium phosphate in dilute hydrochloric 

 acid, this solution, having been neutralised, may be subjected to 

 prolonged dialysis (Maly). (c) Having precipitated by means of 

 alcohol impure pepsin from a glycerin extract of the fundus, the 

 precipitate is dissolved in dilute hydrochloric acid (containing 0'2 per 

 cent, of HC1), and the solution is then dialysed. 



In all these cases it is best to place the dialyser in a running 

 stream of water, the actual form of dialyser being that suggested by 

 Kiihne, in which a tube of parchment-paper contains the solution 

 to be subjected to the process of diffusion. As these tubes are now 

 very frequently made of parchment-paper which is not perfect, it is 

 very convenient to adopt the following plan, which has been com- 

 municated to the author by Mr Benger, of Messrs Mottershead and 

 Co., of Manchester, and which answers admirably. A sheet of De 

 la Rue's parchment-paper is soaked in water, and when thoroughly 

 pliable is drawn together so as to form a bag into which the liquid 

 to be dialysed is poured. The bag is then tied up tightly and sus- 

 pended in a stream of running water. If it be desired to remove 

 the last traces of diffusible substances, such as peptones, from the 

 solution of pepsin, the process of dialysis must be carried on for a 



1 Dr Krasilnikow in 1864 was, according to Hammarsten, the first to make use of 

 dialysis for the preparation of pure solutions of pepsin. 



2 v. Wittich, 'Das Pepsin und seine Wirkung auf Blutfibrin.' Pfliiger's Archiv, Vol. 

 v. p. 435. 



3 Hammarsten, ' Ueber die Indiffusibilitat des Pepsins.' Maly's Jahresbericht, Vol. 

 m. (1874), p. 160. 



