GASTRIC JUICE AND CHANGES IN STOMACH. 155 



mixture to stand a week with frequent shaking, then filter it by aid of the 

 pump. This extract, bottled, will keep many months. For use 5 cc. of 

 it may be diluted with 100 cc. of water containing the right amount of 

 hydrochloric acid, generally O.I to 0.3 per cent. 



For many laboratory experiments a fresh aqueous extract 

 is preferable which may be secured in this manner : 



Ex. The washed mucous membrane of the hog's stomach is chopped 

 fine and then rubbed up in a mortar with sharp sand or powdered glass. 

 Water is added (plus o.i per cent HC1) in amount ten times as great as 

 the weight of the minced membrane, the mixture is thoroughly stirred, 

 and is allowed to stand over night. It is then filtered and is ready for 

 use. Such an extract is relatively strong. 



A much purer product may be secured by the following 

 process as worked out by Kuehne and Chittenden : 



Ex. Remove the mucous membrane of a hog's stomach, wash it thor- 

 oughly with water and spread it out on a plate of glass. Scrape the 

 membrane with a knife or piece of glass and mix the scrapings with hydro- 

 chloric acid of 0.2 per cent strength. About half the membrane should 

 be reduced to the form of scrapings and for this mass 500 cc. of the acid 

 may be used. Allow this to digest at a temperature of 40 C. for about 

 two weeks in order to convert as much as possible of the protein present 

 into peptone. The mixture is filtered, and to the filtrate powdered am- 

 monium sulphate is added to complete saturation. The object of this is 

 to throw down the pepsin and some albumose, the peptone formed in the 

 digestion being left in solution. This precipitate is collected on a filter, 

 washed with saturated ammonium sulphate solution and redissolved in a 

 little 0.2 per cent hydrochloric acid. The solution so obtained is placed 

 in a tube dialyzer with a little thymol water and dialyzed in running water 

 until the sulphate is all removed. The pepsin solution left is mixed with 

 an equal volume of 0.4 per cent hydrochloric acid and kept at 40 C. 5 

 days to complete peptonization of albumose still present. Then precipi- 

 tation with ammonium sulphate to saturation is again effected, the pre- 

 cipitate collected and washed as before and taken up with 0.2 per cent 

 hydrochloric acid. This solution is dialyzed in running water for the 

 removal of all sulphate. The liquid remaining in the dialyzer is a com- 

 paratively pure pepsin solution. It may be concentrated in shallow dishes 

 or on glass plates at a temperature not above 40 C., and leaves finally 

 a scale residue. It may be evaporated perhaps better in shallow dishes 

 placed in a large vacuum desiccator with sulphuric acid. The flakes or 

 scales resulting may be kept in dry form almost indefinitely and will be 

 found extremely active. 



Commercial Pepsin. What is commonly known as pepsin 

 is a product prepared on the large scale from the hog's stom- 



