480 DIGESTION. 



of a knife or an ivory paper-cutter, scrape off all the mucus from 

 the surface. Rub it up in a mortar with clean silicious sand 

 or powdered glass and water, let it stand some time, stirring 

 it from time to time, and then filter it. The filtrate is gastric 

 juice in a state of very considerable purity. It is slightly opa- 

 lescent, and contains a large quantity of pepsin and but little 

 peptone. When acidulated with its own bulk of dilute hydro- 

 chloric acid of 0.2 per cent., it digests fibrin with great rapidity. 

 It may be kept in a bottle for a long time, and though fungi 

 grow on its surface, it still retains its digestive powers. 



A much stronger gastric juice, though not so pure, is ob- 

 tained by scraping the mucus from the stomach as in the first 

 process, or by dissecting off the whole mucous membrane from 

 the muscular layer, cutting it into small pieces, then rubbing 

 it up with dilute hydrochloric acid of 0.1 per cent, and filtering. 

 The gastric juice so readily prepared by this method is very 

 strong, and does very well for experiments on digestion, al- 

 though it contains a good deal of albumin which is dissolved 

 in the acid. It may be freed in a great measure from albumin 

 by putting it into the water-bath at 35 C., for several hours, 

 so as to convert the albumin into peptones, and then transfer- 

 ring it to a dialyzer, and changing the water several times. 

 The peptones will diffuse out into the water, a great part of 

 the pepsin will remain in the dialyzer. 



* 110. To Prepare Hydrochloric Acid containing 

 0.2 per cent, of real HC1. The ordinary strong hydrochlo- 

 ric acid sp.gr. 1.16 contains 31.8 per cent, by weight of HC1. 

 gas. To prepare a dilute acid, containing 0.2 per cent, of real 

 IIC1., measure out with a graduated pipette 6.25 cubic centi- 

 metres of such acid into a litre flask ; fill the flask up to the 

 neck with distilled water, and shake so as to mix thoroughly. 



* 111. To Prepare a Solution of Pepsin in Glycerin. 

 The solubility of digestive ferments in glycerin was dis- 

 covered by Yon Wittich ; and by its means they may be ob- 

 tained with great facility. Cut open the stomach of a pig 

 or rabbit (best when newly killed), and wash the mucous 

 membrane as directed ; cut off the pyloric part ; stretch the re- 

 mainder on a piece of board, and dissect off the mucous mem- 

 brane from the muscular layer. Cut up the mucous membrane 

 into small pieces and put it into a beaker, with sufficient gly- 

 cerin to cover it. It will acquire peptic properties in a few- 

 hours, but it is as well to let it remain for several days. Then 

 strain off the glycerin and put on a fresh quantity. This may 

 be repeated several times, and each time the glycerin will take 

 up a fresh quantity of pepsin. 



An artificial gastric juice may be readily prepared whenever 

 s wanted by adding a little of the glycerin extract to hydro- 

 chloric acid of 0.1 per cent. 



