23 



solution of formalin. The solution will keep indefinitely, 

 and remains active. For use take, after filtering through 

 absorbent cotton, i cc. of this extract and add to it 6-8 cc. 

 of 0.2% hydrochloric acid in a test-tube. 



99. Glycerin extract of pep.sin. Add to the minced mu- 

 cosa, 2-3 times its weight of pure concentrated glycerine. 

 Let it stand for a week or ten days, shaking it frequently. 

 The pepsin is soluble in the glycerin and the extract thus 

 prepared will keep for a long time. When ready to use 

 strain through muslin and filter through absorbent cotton. 

 Add hydrochloric acid as in 98. 



100. Acidulated extract of pepsin. Mince the mucosa 

 very finely. Add to it, in a flask, fifty times its weight of 

 0.2% hydrochloric acid and put in the incubator for 12 

 hours. This is a solution of pepsin in hydrochloric acid, and 

 is quite powerful in its action. The solution also contains 

 peptones, but these may be eliminated by dialysis. 



loi. For this exercise there have been prepared extracts 

 of the gastric mucosa from the pig (omnivorous), and the 

 cat or dog (carnivorous). , 



Label 5 test tubes. A, B, C, D. E, for the omnivorous ex- 

 tract, and for the carnivorous extract. A', B', C, D', E', In 

 A fill the tube half full of distilled water, and add 30 drops, 

 or 2 cc. of the extract. Fill B half full of 0.2% hydrochloric 

 acid. Treat C similarly to B, but add 30 drops of the ex- 

 tract. Fill D half full of a i % solution of sodium carbonate 

 and add 30 drops of the extract. Place 30 drops of the ex- 

 tract in E and add 2 or 3 cc. of distilled water and boil, then 

 add enough 0.2'fo hydrochloric acid to make the tube half full. 

 Treat A', B', C, D', E' in the same way with the carnivorous 

 extract. In each of the 10 test tubes put a small thread of 

 well- washed and boiled fibrin. Place all the tubes in a water 

 bath at 40° C. , and after an hour note any changes that may 

 have occurred in any of the tubes. The rapidity of action 

 will indicate the strength of the ferment. Explain in your 



