DIGESTION AND ABSORPTION. 175 



Tube (k) 0.025%: Add 2.5 c. c. of 0.1% HC1 and aq. 



dist. q. s. ad 10 c. c. 

 Tube (1) 0.01%: Add 1 c. c. of 0.1% HC1 and aq. dist. 



q. s. ad 10 c. c. 

 Tube (m) 0.005%: Add ^ c. c. of 0.1% HC1 and aq. 



dist. q. s. ad 10 c. c. 



Place these twelve tubes in the incubator and note 

 conditions every 10 minutes for the first hour, every 

 hour for the first six hours and then at the end of one 

 or two days make the final observations. 



Tabulate results. Formulate conclusions. What 

 range of strength may, from the experiments with 

 artificial gastric juice under artificial conditions, be 

 considered the optimum strength for the acid? Is 

 there any reason to doubt that the optimum strength 

 as determined above is essentially different from the 

 optimum strength in normal digestion ? 

 (8) To determine how dilute the pepsin may be and still 

 be efficient in digestion. 



This experiment requires a standard solution of 

 pepsin to use as a basis. The U. S. Pharmacopoeia 

 (p. 295 of the 7th Decennial Revision) gives the fol- 

 lowing formula for a standard solution of pepsin: 

 Hydrochloric acid (absolute), 0.21 gm. 

 Pepsin (pure), 0.00335 gm. 

 Water (distilled), q. s. ad 100 c. c. 



The following suggestions are made as to method 

 of preparation: To 294 c. c. of water add 6 c. c. of 

 dilute hydrochloric acid: SOL. A.* 



In 100 c. c. of Sol. A. dissolve 0.067 gm. of standard 

 pepsin: SOL. B. To 95 c. c. of Sol. Aat 40C. add 5 c. c. 



*HC1. DIL. contains 10$ of Abs. HC1. The C. P. muriatic acid of 

 standard Sp. Gr. contains 31.9$ Abs. HC1. 



