LESSON XVIII 



DIGESTION 



1. Activity of Pepsin Solutions (Griitzner's Method). Examine the com- 

 parative 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 

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

 the more active preparation of pepsin. 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 till 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 till the washings are colourless. 

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



'2. Mett's Tubes. A method which is now more generally employed for 

 estimating the proteolytic activity of a digestive juice is one originally 

 introduced by Mett. Pieces of capillary glass tubing of known length are 

 filled with white of egg. This is set into a solid by heating to 95 C. They 

 are then placed in the digestive fluid at 36 C., and the coagulated egg-white 

 is digested. After a given time the tubes are removed ; and if the digestive 

 process has not gone too far, only a part of the little column of coagulated 

 protein will have disappeared ; the length of the remaining column is easily 

 measured, and the length that has been digested is a measure of the digestive 

 strength of the fluid. 1 This forms a very convenient method to use in experi- 

 ments on velocity of reaction. Schutz's Law states that the amount of action 

 is proportional to the square root of the amount of ferment. If this rule 

 applies (which is doubtful) it applies only to the action of pepsin hydrochloric 



1 Hamburger has used the same method in investigating the digestive action of 

 juices on gelatin. The tubes are filled with warm gelatin solution, and this jellies 

 on cooling. They are placed as before in the digestive mixture, and the length of 

 the column that disappears can be easily measured. These experiments must, how- 

 ever, be performed at room temperature, for the usual temperature (36 C -40 C.) at 

 which artificial digestion is usually carried out would melt the gelatin. He has also 

 used the same method for estimating amylolytic activity, by filling the tubes with 

 thick starch paste. 



