140 THE DIGESTIVE FLUIDS. 



adult vertebrate animals, it is noteworthy that it is absent from the 

 gastric juice of sucking pups, as shown by Gmelin ; that its presence, 

 moreover, is not essential to the maintenance of life is shown by the 

 history of Czerny's dog and Hoffmann's observations in the case of 

 a woman whose stomach had been removed in toto. 



Specific tests for the demonstration of the pepsin of the gastric 

 juice, as compared with other proteolytic ferments which similarly 

 act in acid solutions, are unknown. As a result, all such ferments 

 have been designated as pepsin, although it is very likely that they 

 are not identical. Such ferments have been observed in the secre- 

 tion of the glands of Brunner, in the muscles, the kidneys, the 

 brain, the saliva, and the urine. 



Isolation of Pepsin. If it is merely desired to obtain an effective 

 solution of pepsin without regard to the purity of the substance, 

 the following procedure may be employed: 



v. WITTICH'S METHOD. The mucous membrane of a pig's 

 stomach is carefully dissected off, freed from mucus by washing 

 with water, hashed, rubbed together with pure quartz sand, and 

 finally treated with glycerin, containing 0.1 per cent, of hydrochloric 

 acid, in the proportion of 10-20 grammes for 1 part of mucous 

 membrane. The mixture is kept at a temperature of 40 C. for 

 from one to two weeks, when it is filtered. The extract which is 

 thus obtained may then be used for experimental purposes by 

 diluting with 0.10.4 per cent, of hydrochloric acid, in the propor- 

 tion of 2-3 : 100. For the preparation of a pure pepsin the follow- 

 ing method should be employed : 



PEKELHARING'S METHOD. Gastric juice uncontaminated by 

 food-material or saliva is obtained from dogs that have been operated 

 according to Pawlow's method (stomach and oasophageal fistulse). 

 The gastric juice obtained in portions after pseudofeeding, is filtered 

 and dialyzed for about twenty hours against distilled water, at a 

 temperature not much above C. A portion of the pepsin is thus 

 precipitated and isolated by centrifugation. It is collected on a 

 filter, washed with a little distilled water, and dried in the desiccator. 

 The liquid portion of the original material, after centrifugation is 

 half-saturated with ammonium sulphate (35 grammes for 100 c.c.). 

 The resulting precipitate is freed from salt by dialysis, dissolved in 

 0.2 per cent, hydrochloric acid, reprecipitated by dialysis, collected 

 on a filter, and dried. 



Quantitative Estimation of Pepsin. Accurate methods for the 

 quantitative estimation of pepsin are not available. Relative values, 

 however, can be obtained by the following method, as suggested by 

 Mett: 



Capillary glass tubes are prepared measuring from 1 to 2 mm. in 

 diameter. They are filled with white of egg, which is coagulated 

 in the tubes at a temperature of 95 C. The tubes are then cut into 

 pieces from 1 to 2 cm. long and placed in the digestive mixture to 

 be examined. The length of the column digested in a given length 



