GASTRIC DIGESTION. 77 



Where the membrane has been for some time exposed to the 

 air before extracting the active enzyme may have been formed 

 and consequently no difference be perceptible. 



182. To make a pepsin solution which may be pre- 

 served, though it is somewhat impure, chop the mucous 

 membrane finely, as in the previous methods, and after 

 squeezing it in a piece of cloth to remove the water as 

 far as possible, cover it with two or three times its volume 

 of glycerin and let it stand for a week. Filter it through 

 a piece of muslin, pressing out the glycerin. This gives a 

 permanent solution which can be used at any time for 

 digestive experiments. 



183. In each of a series of test tubes standing in a beaker of 

 water at 38 place a little pepsin solution and a shred of fibrin. 

 Then add to (a) lactic acid up to 0.8 per cent.; (b) oxalic acid up 

 to 1 per cent.; (c) hydrochloric acid to 10 per cent; (d) hydro- 

 chloric acid to 0.2 per cent. ; but wrap the fibrin tightly with fine 

 thread so that it cannot swell, (e) 0.2-per-cent. hydrochloric acid. 

 Note the speed of digestion. 



184. Make an artificial gastric juice by preparing 

 a 0.2-per-cent. solution of hydrochloric acid as in Experi- 

 ment 179, and adding to this a small quantity of the 

 glycerin solution of pepsin. The solution made directly 

 with the dilute acid can be used if it is fresh. To this add 

 a small handful of washed fibrin. If this is not at hand, 

 boiled egg-albumin may be substituted for it, though in 

 this case the digestion is slower. Warm the mixture care- 

 fully to about body-temperature and keep it at this point 

 until the albuminous substance has dissolved. Notice 

 that the edges first become transparent, then are dissolved. 

 Too high heat will destroy the ferment. The fibrin should 

 be nearly digested in half an hour. It may.be left for 



