132 BACTERIOLYSINS AND HEMOLYSINS 



however, the normal serum has no influence upon the bacteria, so that 

 they increase rapidly and kill the animal. 



It is evident then, that the bacteriolytic power resides not only in the 

 actively immunized animal, but that it may also be transmitted to other 

 animals by means of the former's serum. Bacteriolysis, therefore, is not a 

 property of the tissues of the actively immunized animal, but is to be traced 

 to specific antibodies, "Bacteriolysins" which circulate in the blood 

 serum and body fluids. 



From the above experiment it must be assumed that the phenomenon 

 of bacteriolysis, like agglutination and precipitation, can be demonstrated 

 also in vitro. The earlier investigations in this connection, however, 

 were unsuccessful. Bordet was the first to obtain conclusive results and 

 also to elucidate the cause of previous failures. 



While agglutination in vitro and bacteriolysis in 'vivo were 

 Bacteriolysis readily produced by mixing living bacteria with old immune 

 in Vitro, serum, bacteriolysis in vitro did not occur under similar cir- 

 cumstances. But when freshly drawn blood serum or exudate 

 of an immune animal was used, bacteriolysis took place in vitro also. 

 (In fact, granule formation can be directly observed by the microscope.) 

 When the serum becomes old and twenty-four hours is sufficient to 

 cause the change, it loses its bacteriolytic powers. It seems at first 

 glance as if bacteriolysins may be active outside the body also, but that 

 here they lead only an ephemeral existence. This view, however, is not 

 quite correct; for " inactive" serum, which has become "ineffective" in 

 vitro, can again produce bacteriolysis, if it is utilized to passively immu- 

 nize healthy animals. Something must exist in the organism, which 

 supplements the inactive bacteriolysins and restores their activity. This 

 "reactivating substance" is independent of the immunizing process, since 

 it is to be found in normal animals also. Furthermore, inasmuch as 

 not only cholera and typhoid immune sera, but also all other immune 

 sera and not only guinea-pig's serum but even rabbit's, horse's, and human 

 serum may in like manner be reactivated, it is evident that the reactivat- 

 ing agent lacks specificity. On account of this peculiar quality of supple- 

 menting the inactive bacteriolytic serum so that it can develop its real 

 effectiveness, Ehrlich called the reactivating substance "Complement." 

 Accordingly, the complement is a normal non-specific substance which is found 

 in the body fluids (particularly abundant in the blood serum) oj every organism; 

 its existence is evidenced either by the activation or reactivation of bacteriolytic 

 antibodies. 



Bordet demonstrated that the apparent ease with which the bac- 

 teriolysins lose their activity is to be traced not to these bodies, but to 

 the complement. If a small amount of fresh normal serum is added to 

 bacteriolytic serum which has become inactive, reactivation occurs in 



