ANTIGENS AS BIOCATALYSTS 41 



ordinary conditions it does not clot milk. Chymotropsin, on the other 

 hand, clots milk but not blood. It probably represents the pancreatic 

 rennin of Vernon. Trypsin appears to be identical in its specificity with 

 Waldschmidt-Leitz's "Proteinase." 



Sensitization of Guinea Pigs. The antibody production by the above 

 enzymes and pro-enzymes was tested by anaphylactic test. This test, 

 rather than the less sensitive precipitin reaction, was used in the major 

 portion of the tests for differentiation for the reason that the enzymes 

 may be very closely related. Since the sensitization of an animal 

 is tantamount to immunization and anaphylactic shock depends upon 

 an antigen-antibody reaction, the anaphylactic reactions have the 

 same significance for the question under consideration as the precipitin 

 reaction in vitro (Landsteiner, 1936). Female guinea pigs weighing 

 about 125 g. were given subcutaneous injections of 0.5 ml. of either 

 0.5 or 1 per cent solution of the enzymes, purified by five crystal- 

 lizations. Injections of chymotrypsinogen produced no visible effect, 

 but the animals receiving the trypsin and chymotrypsin showed 

 necrotic areas at the site of inoculation, and several of them died. 

 Chymotrypsin seemed to be more toxic than trypsin. Between 15 

 and 20 days after the first injection the uteri of these guinea pigs 

 were tested by means of the Dale technique (Dale, 1931). Two baths 

 were used and the two horns of the uterus were tested, one after the 

 other. The capacity of each bath was 75 ml. and 0.75 mg. of the en- 

 zyme solution was added for each test (1 : 1000 dilution of the enzyme 

 in the bath). The uteri of guinea pigs receiving pig trypsin injections 

 did not react against beef trypsin and chymotrypsin in 1 : 1000 con- 

 centrations; on the other hand, pig trypsin showed definite positive 

 reactions with both left and right horns of the guinea pig uterus sensi- 

 tized with pig trypsin. In three groups of similar tests the results 

 showed that (1) guinea pigs receiving beef trypsin were sensitized 

 against itself, but not against chymotrypsin and chymotrypsinogen; 

 (2) guinea pigs receiving chymotrypsinogen were sensitized against 

 itself but not against chymotrypsin and beef trypsin; and (3) guinea 

 pigs receiving chymotrypsin were sensitized against itself, but not 

 against chymotrypsinogen. Ten Broeck makes the following state- 

 ment as a summary of his studies: "Not all of the animals were sensi- 

 tized, and in some cases there were cross-reactions, particularly between 

 the chymotrypsin and chymotrypsinogen. The results were, however, 



