GASTRIC DIGESTION. 37 



the last particle in a quarter- to a half-hour, and the slice of 

 egg-elbumen should be perceptibly diminished after an hour 

 if pepsin is present. 



IV. INFLUENCE OF THE QUANTITY OF PEPSIN ON DIGESTION. 



Prepare an artificial digestive fluid from commercial pep- 

 sin and dilute hydrochloric acid (0.27 per cent.). If pepsin, 

 which will dissolve in water forming a clear or almost clear 

 solution, is to be had, dissolve 0.5 g. of it in 500 cc. of dilute 

 hydrochloric acid (the hydrochloric acid used for digestion 

 experiments is always a mixture of 6 cc. of strong hydro- 

 chloric acid, sp. gr. 1.19, with 994 cc. of water, i.e., 6 cc. 

 of hydrochloric acid diluted to one liter: the solution desig- 

 nated on page 33 as hydrochloric acid solution A). If 

 only the pepsin insoluble in water is available, which may 

 nevertheless be very active, treat 0.5 g. of this with water, 

 stir thoroughly, and wash with water until the filtrate no 

 longer gives the reaction for milk-sugar. After piercing the 

 filter, wash the residue into a flask with 100 cc. of the 0.27 

 per cent, hydrochloric acid, let stand with frequent agita- 

 tion for twenty-four hours at the room temperature or at 

 40, filter, and dilute with solution A to one-half of a liter. 



Put into each of three test-tubes, A, B, and C, approxi- 

 mately equal quantities of fibrin, 1 preferably weighed quan- 

 tities (about 1 g.). To A add 10 cc. of the dilute hydrochloric 

 .acid (0.27 per cent.), to B 5 cc. of the same hydrochloric 

 acid and 5 cc. of the pepsin hydrochloric acid solution, to C 

 10 cc. of the pepsin hydrochloric acid, and place the tubes in 

 .a water-bath at 40. The fibrin in Aswel's, but does not dis- 

 solve; in B and C it dissolves, and more quickly in C than in 

 B. If the pepsin used is very active it may happen that no 



1 Instead of fresh fibrin we may also use here the fibrin which has been 

 kept in glycerin, after it has been freed from the glycerin clinging to it by 

 washing thoroughly with water. 



