38 PHYSIOLOGICAL AND PATHOLOGICAL CHEMISTRY. 



difference between B and C is perceptible; then more dilute 

 solutions are to be used. 



The experiment may also be performed by placing the fibrin and 

 the dilute hydrochloric acid (0.27 per cent.) in all the tubes, adding 

 nothing to A, to B 2 drops of a glycerin extract of a pig's stomach, 

 and to C 4 drops of the same extract. According to Griitzner the 

 difference may be more readily perceived if we use fibrin colored with 

 carmine. In order to color the fibrin let it lie for twenty-four hours 

 in a 1 per cent, solution of carmine (rendered as nearly neutral as 

 possible by evaporating the ammonia) and then wash the fibrin with 

 water. 



V. INTERFERENCE OF CERTAIN SUBSTANCES WITH 

 DIGESTION. 



Dissolve 2.5 g. of gum arabic, by shaking for some rae r 

 without heating, in 10 cc. of pepsin hydrochloric acid (A!). 

 In an equal amount of the pepsin hydrochloric acid dissolve 

 5 g. of cane sugar (B'). A third portion is prepared without 

 any addition (C'). In each of these tubes put 1 g. of fresh 

 fibrin (or of the fibrin preserved in glycerin, after it has been 

 well washed and drained), and digest at 40. In C' the fibrin 

 dissolves quickly, slowly in B', and still more slowly in A'. 

 Many other indifferent substances, which have no affinity for 

 hydrochloric acid, may also retard digestion. 



VI. COMPARISON OF THE DIFFERENT KINDS OF COMMERCIAL 



PEPSIN. 



The method is somewhat different according as the pepsin 

 is soluble in water or not. In the first case 1 g. is dissolved 

 directly in 500 cc. of 0.27 per cent, hydrochloric acid. In 

 the second case 1 g. is freed from milk-sugar as directed 

 under IV, page 37, and then washed into a flask with 500 cc. 

 of 0.27 per cent, hydrochloric acid (or it may also be treated 

 directly, without any previous washing, with the 0.27 per 

 cent, hydrochloric acid), digested in this for twenty-four hours 

 at room temperature or at 40, and then filtered through a 



