PEPSIN. 469 



perature within a couple of days. Upon the addition of a little pepsin, 

 however, this swollen mass dissolves quickly at ordinary temperatures. 

 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 pres- 

 ence of pepsin causey the edges to become clear and transparent, blunt 

 and swollen, and the protein gradually dissolves. 



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

 proteins may be employed as a means of detecting pepsin in liquids. 

 Ox-fibrin may be employed as well as coagulated egg albumin, 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 explana- 

 tion we ordinarily understand it as the test with fibrin. 



This test, nevertheless, requires care. The fibrin used should be 

 ox-fibrin and not pig-fibrin, which last is dissolved too readily with dilute 

 acid alone. The unboiled ox-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 temperature of the body unboiled fibrin is more easily 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 condi- 

 tion, it is impossible to determine the absolute quantity of pepsin in a 

 liquid. It is possible only to compare the relative amounts of pepsin 

 in two or more liquids, which may be done in several ways. 



The older method, that of BRUCKE, consists in diluting the two pepsin solu- 

 tions to be compared with certain proportions of 1 p. m. hydrochloric acid, so 

 that when the amount of pepsin contained in the original solution is equal to 1, 

 each solution contains a degree of dilution, p, corresponding to 1, $, i, f, &, 

 etc. A flock of fibrin or a piece of hard-boiled egg is added to each test and the 

 time noted when each test begins to digest and when it ends. The relative 

 amount of pepsin is calculated from the rapidity of digestion as follows: The tests 

 P = i> !> TGJ f ne series is digested in the same time as tests p = l, %, \ of the 

 other series, hence the first solution contained four times as much pepsin. 

 GRUTZNER l has improved this test by using fibrin colored with carmine, and on 

 comparing with carmine solutions of known dilution he determines colorimetrically 

 the rapidity of digestion. 



METT'S Method. Draw up white of egg in a glass tube 1-2 millimeters in 

 diameter, coagulate it by plunging it into water at 95 C., and cut the ends off 

 sharply; then add two tubes to each test-tube with a few cubic centimeters 

 of the acid pepsin solution; allow them to digest at body temperature, and after 

 a certain time, generally, after ten hours, measure the lineal extent of the digested 



1 Griitzner, Pfliiger's Arch., 8 and 106. See also A. Korn, " Ueber Methoden Pepsin 

 quantitativ zu bestimmen," Inaug.-Dissert., Tubingen, 1902. 



