294 INFECTION AND IMMUNITY 



sterile "aggressin" exudates could be shown to possess a considerable 

 degree of toxicity and because the aggressive action could be duplicated 

 by aqueous extracts of bacteria. Citron, 1 was able to show, by the 

 Bordet-Gengou method of complement fixation, thaf '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 2 has done certain experiments 

 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 offensive weapons on the part of 

 bacteria, it is certainly a fact that microorganisms differ much in their 

 powers of defense against destruction 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 anti- 

 bodies and the bacterial protein may produce toxic substances 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. 



1 Citron, Cent. f. Bakt., I, xl, 1905; xli, 1906; and Zeit. f. Hyg., lii, 1905. 



2 Zinsser and Dwyer, Proceedings of theSoc. forExper. Biol.and Mcd., 1914, xi, 74-76. 



