IMMUNITY, IMMUNIZATION, AND CURE. 59 



when the bacteria gain dominance. That the leukocytes 

 not only incorporate the bodies of dead bacteria, but also 

 take up living microbes, to destroy them later, can, like- 

 wise, no longer be doubted, since Metschnikoff observed in 

 the hanging drop how anthrax-bacilli, already inclosed 

 within phagocytes, still developed, multiplied, and produced 

 virulent cultures. It is possible, also, that a number of 

 methods of immunization, in which relatively simple pro- 

 tective fluids are employed, induce their effects especially 

 through phagocytosis. Thus, for instance, intraperitoneal 

 injection of normal blood-serum, of physiologic salt-solu- 

 tion, of bouillon and other substances, by means of which 

 it is possible to protect guinea-pigs against an otherwise 

 lethal injection of cholera-vibrios, are powerful stimulants 

 of phagocytosis. 



In the interpretation of his observations Metschnikoff 

 has, however, gone altogether too far. The inflammatory 

 local reaction is, in the case of infections that pursue a favor- 

 able course, present, it is true, and prognostic conclusions 

 may even be formulated from its occurrence ; but besides 

 phagocytosis and in this the opponents of Metschnikoff 

 must be conceded to be correct other factors enter into 

 play. Among these are the bactericidal or antidotal prop- 

 erties that can be demonstrated to be present in the tissue- 

 fluids, especially in the blood-serum of immune, and, in 

 greater degree still, of immunized animals. These are to 

 be attributed to a number of substances that, although thus 

 far not chemically defined, are distinctly differentiable ac- 

 cording to their physiologic activities. These are appro- 

 priately grouped together as ANTI-BODIES. They may be 

 divided into (i) bactericidal, (2) lysogenic, (3) agglutinating, 

 and (4) antitoxic substances. 



i. BACTERICIDAL SUBSTANCES. The property of the 

 bodily fluids to destroy bacteria and inhibit their activity 

 was first observed when microorganisms as a rule anthrax- 

 bacilli were introduced into immune animals, and the bac- 

 teria were, after a time, seen to undergo degeneration at 

 the site of inoculation. To establish the certainty that the 

 living cells did not participate in this process, the anthrax- 

 bacilli were introduced inclosed in paper bags and the like. 

 In the experiments thus conducted various investigators 

 observed degeneration of the inoculated anthrax-bacilli, 

 and in some instances even destruction of their spores. 



