GASTRIC JUICE AND CHANGES IN STOMACH. 157 



at a low temperature, pour it in a test-tube and add some strong alcohol. 

 This gives a precipitate of peptone, which dissolves by adding water. The 

 intensity of the peptone reaction depends on the duration of the digestion. 

 By preparing a number of mixtures and keeping them at a temperature of 

 40 for different periods different results will be obtained. It is an in- 

 structive exercise to test samples of commercial pepsin in this way. For 

 such tests about 10 milligrams should be used. 



In practice pepsin, is always valued by the amount of protein 

 matter it will digest in a given time. Hard-boiled white of 

 egg is generally employed with hydrochloric acid of 0.2 per 

 cent strength. Sometimes w r ell-washed fibrin is used, with a 

 somewhat weaker acid. As an illustration of practical pepsin 

 testing the following may be given, which is essentially the 

 process of the U. S. Pharmacopoeia : 



VALUATION OF PEPSIN. 



Prepare an acid solution by diluting 57.6 cc. of normal volumetric hydro- 

 chloric acid to make 500 cc. 



In 500 cc. of water dissolve 0.0335 gm. of pepsin. 



Mix 50 cc. of the acid solution with 50 cc. of the pepsin solution. The 

 resultant 100 cc. will contain 0.21 gm. of actual hydrochloric acid and 

 0.00335 gm. of pepsin. 



Boil a fresh hen's egg fifteen minutes, then cool it by placing in cold 

 water. Separate the coagulated white part and rub it through a clean 

 sieve having 30 meshes to the linear inch. Reject the first portions which 

 pass through. Weigh out exactly 10 gm. of the clean disintegrated sub- 

 stance, place it in a 200 cc. flask and add 100 cc. of the acid-pepsin mix- 

 ture last described. Put the flask in a large water-bath or thermostat 

 kept at 38-4O C. and let it remain six hours, shaking gently every fifteen 

 minutes. At the end of this time the albumin should have practically 

 disappeared, leaving at most only a few insoluble flakes. Much depends 

 on keeping the temperature constant, and shaking at regular intervals. 

 The Pharmacopoeia allows a latitude of 2, but in exact comparative work 

 it is better to keep the bath exactly constant at 40. 



In the above test if the albumin is all digested it shows that the pepsin 

 has a converting power of 3,000 or over, which meets the practical require- 

 ment of the Pharmacopoeia. The relative digesting power of stronger or 

 weaker pepsin may be ascertained by finding through repeated trials how 

 much of a pepsin solution mixed with the acid and made up to 100 cc. 

 will be required to dissolve the 10 gm. of disintegrated white of egg 

 under the same conditions. The process, although not thoroughly satis- 

 factory, is a good one for practical purposes. 



