180 PHYSIOLOGICAL CHEMISTRY. 



the addition of a little pepsin, however, this swollen mass dissolves, 

 quickly at an ordinary temperature. Hard-boiled-egg albumin, cut 

 in thin pieces with sharp edges, is not perceptibly changed by dilute 

 acid (2-4 p. m. HC1) at the temperature of the body in the course 

 of several hours. But the simultaneous presence of pepsin causes 

 the edges to become clear and transparent, blunt and swollen, and 

 the albumin gradually dissolves. 



From what has been said above in regard to pepsin, it follows 

 that albumin may be employed as a means of detecting pepsin in 

 liquids. ' Fibrin may be employed as well as hard-boiled-egg albu- 

 min, which latter is used in the form of slices with sharp edges. 

 As the fibrin is easily digested at the normal temperature, while 

 the pepsin test with egg-albumin requires the temperature of the 

 body, and as the test with fibrin is somewhat more delicate, it is 

 often preferred to that with egg-albumin. When we speak of the 

 "pepsin test" without further explanation, we ordinarily under- 

 stand it as the test with fibrin. 



This test nevertheless requires care. The unboiled fibrin may 

 be dissolved by acid alone without pepsin, but this generally 

 requires more time. In testing with unboiled fibrin at normal 

 temperature, it is advisable to make a control test with another 

 portion of the same fibrin with acid alone. Since at the tempera- 

 ture of the body unboiled fibrin is easier dissolved by acid alone, it 

 is best always to work with boiled fibrin. 



As pepsin has not, thus far, been prepared in a positively pure 

 condition, it is impossible to determine the absolute quantity of 

 pepsin in a liquid. It is only possible to compare the relative 

 amounts of pepsin in two or more liquids, which may be done in 

 several ways. As the best of these we give the following method 

 as suggested by BRUCKE. 



If two pepsin solutions A and B are to be compared with each other 

 relatively to the amounts of pepsin they contain, they must first be brought 

 to the proper degree of acidity, about 1 p. m. HC1, care being taken that one is 

 not more diluted than the other. Then prepare a large number of specimens 

 of each solution by diluting with hydrochloric acid of 1 p. m. HC1, so that they 



contain respectively ^, , , ^, $, and so on, the amount of pepsin in the 

 original liquid being 1. If the original quantity of pepsin in the two liquids 

 is designated by p and p', we then have the two series of liquids : 



A 

 lp 



