158 FUNCTIONS OF NUTRITION. 



months without developing any putrescent odor or losing its character- 

 istic properties. It becomes somewhat darker in color, and after a time 

 deposits a brownish sediment, but retains its acid reaction and its power 

 of digesting albuminous matters. It will even arrest putrefactive 

 changes which have already begun in organic substances ; and conse- 

 quently putrefaction does not go on in the living stomach. Beaumont 

 preserved fragments of meat unaltered for a month in gastric juice, 

 while other portions kept in saliva were putrefied in ten days. Spal- 

 lanzani found in the stomach of a viper the body of a lizard which had 

 remained there for sixteen days without putrefactive alteration ; and 

 similar observations have been made by other physiologists. Accord- 

 ing to Richet, the antiseptic property of gastric juice depends entirely 

 on its free acid, and not in any degree on its organic ferment. 



Pepsine Extracts, and Artificial Digestive Fluids. As the imme- 

 ^liate source of the gastric juice is the mucous membrane of the stomach, 

 the idea was early suggested that a similar fluid might be extracted 

 from its tissue after death. Experiments of this kind have been made 

 in various ways since 1834 ; and they have demonstrated that' the 

 gastric mucous membrane, taken from the recently-killed animal, may 

 yield a solution containing pepsine, which, in the presence of a dilute 

 acid, at the proper temperature, has the power of dissolving solid albu- 

 minous matters. Such solutions act as artificial digestive fluids, and 

 by their use much additional light has been thrown on the digestive 

 process. They are obtained, according to Lchmann's- method, by 

 immersing the cleansed mucous membrane in water for an hour or 

 two, until moderately softened, when its glandular parts are removed 

 by scraping with a spatula, placed in acidulated water, the mixture kept 

 for an hour at the temperature of 35 C. and the fluid then filtered. 

 Or the mucous membrane may be cut into small pieces, and kept in a 

 large quantity of acidulated water at 35 C. until the glandular tissue 

 is fully disintegrated, when the mixture is filtered and the clear liquid 

 used for experiment. The second process yields a fluid which has con- 

 siderable digestive activity, but is contaminated with products of the 

 digestion of the stomach tissues. The most convenient and most 

 widely employed method is that of Yon Wittich, which consists in 

 extracting the mucous membrane with glycerine. It has the advantage 

 that glycerine, in the concentrated form, while it dissolves out the pep- 

 sine, arrests completely both digestive and putrescent alterations. The 

 'extract finally obtained is therefore free from the products of digestion, 

 and may be kept indefinitely for experimental use. In this process the 

 mucous membrane, cut into small pieces and freed from water by a 

 short immersion in alcohol, is placed in a quantity of glycerine suffi- 

 cient to cover it and macerated for eight days at ordinary temperatures, 

 after which the glycerine solution is strained off. This glycerine 

 extract contains pepsine, and a little of it added to acidulated water 

 forms an efficient digestive fluid. If desired, the pepsine may be pre- 

 cipitated from the glycerine solution by alcohol in excess, removed by 



