OP8ONINS AND VACCINE THERAPY 351 



aggressive action could be duplicated by aqeous extracts of bacteria. 

 Citron, 39 was able to show, by the Bordet-Gengou method of com- 

 plement fixation, that the exudates ,of Bail contained quantities of 

 free bacterial receptors, which, in taking up immune body, would 

 neutralize any destructive power on the part of the infected animal. 



The writer in conjunction with Dwyer 40 has done certain experi- 

 ments which seem to indicate that Bail's aggressin may be in the 

 nature of anaphylatoxin. The addition of such anaphylatoxin to 

 bacteria will convert a sublethal into a lethal dose, as will Bail's 

 aggressin, and in principle the manner of production is the same. 

 The nature of the immunity produced in animals by Bail's method 

 of treatment is less easily explained and less exposed to adverse 

 criticism. Whatever may be the truth about the possession of offen- 

 sive weapons on the part of bacteria, it is certainly a fact that 

 microorganisms differ much in their powers of defense against de- 

 struction by the cells in sera of the animal body. Virulent bacteria 

 are not destroyed by serum or agglutinated or taken up by leucocytes 

 as easily as are the non-virulent. In some cases there seems to be 

 no morphological clue to the reason for this. In other cases, like 

 pneumococci, Friedlander bacilli and others, there is a bacterial 

 capsule which seems to insulate these organisms against attack. 

 Many bacteria lose their capsules in" the non- virulent stage on 

 culture media, but form them within the animal body in the process 

 of infection. Again, bacteria rendered non-virulent by cultivation 

 on artificial media may become virulent, inagglutinable, and more 

 resistant to phagocytosis when cultivated on immune sera or passed 

 through the animal body. 



Thus the power to invade depends possibly upon a combination 

 of offensive properties and defensive qualities on the part of the 

 bacteria. Added to this, some of us believe that the reaction between 

 lytic antibodies and the bacterial protein may produce toxic sub- 

 stances which poison the animal body, prevent positive chemotaxis, 

 and thereby aid the invader. 



Again, there are microorganisms like the treponema pallidum in 

 syphilis where adaptation between invader and host seems to be of 

 such a nature that an indifferent reaction against the invading 

 organism only is set up. 



39 Citron, Cent, f . Bakt., I, xl, 1905 ; xli, 1906 ; and Zeit. f . Hyg. Hi, 1905. 



40 Zinsser and Dwyer, Proceedings of the Soc. for Exper. Biol. and Med., 1914, 

 xi, 74-76. 



