149 



LESSON XVIII 

 DIGESTION 



1. Activity of pepsin solutiona. Exauune the comparative digestive 

 power of the glycerin extracts of two stomachs. Take in two test-tubes an 

 equal small weighed quantity of fibrin stained with carmine. Add to each 

 10 c.c. of 0*2-per-cent. hydrochloric acid. Add to one a measured quantity of 

 one glycerin extract, and to the other an equal quantity of the other glycerin 

 extract. As the fibrin is digested the carmine is set free, and coloxurs the 

 liquid ; that which is more deeply stained is that which contains the more 

 active preparation of pepsin. 



This exercise illustrates the principle of Griitzner's method of comparing 

 the digestive powers of solutions. In the original method the amount of 

 carmine set free is estimated by an artificial scale consisting of ten solutions 

 of carmine of different known strengths. 



The carmine solution for staining the fibrin is prepared by dissolving 

 1 gramme of carmine in about 1 c.c. of ammonia ; to this 400 c.c. of water 

 are added, and the mixture is kept in a loosely stoppered bottle tUl the smell 

 of ammonia has become faint. 



The fibrin is stained by taking it perfectly fresh and clean. It is chopped 

 finely and placed in the carmine solution for twenty-four hours. The fluid is 

 strained off and the fibrin washed in water tUl the washings are colourless. It 

 is kept in a stoppered bottle with just enough ether to cover it. 



2. Tests for Free Hydrochloric Acid, (a) Gunsberg's reagent consists of 2 

 parts of phloroglucrnol, 1 part of vanillin, and 30 parts of rectified spirit. A 

 drop of filtered gastric juice is evaporated with an equal quantity of the 

 reagent. Eed crystals form, or if much peptone is present, there will be a red 

 paste. The reaction takes place with 1 part of hydrochloric acid in 10,000. 

 The organic acids do not give the reaction. 



(6) Tropaeolin test. Drops of a satmrated solution of tropaeolin-00 in 94 

 per cent, methylated spirit are allowed to dry on a porcelain slab at 40° C. 

 A drop of the fluid to be tested is placed on the tropaeolin drop, still at 40° C. ; 

 -and if hydrochloric acid is present, a violet spot is left when the fluid has 

 evaporated. A drop of 0*006 per cent, hydrochloric acid leaves a distinct 

 mark. 



(For a very complete account of these and other colour reactions see 

 ■* Diseases of the Stomach,' chap. v. By Sidney Martin, F.E.S. 1895.) 



3. Fancreatie Digestion. A finely divided ox-pancreas has been allowed 

 4o digest at 40° C. for twenty-four to thirty-six hours in a litre of 1 per cent. 



