294 INFECTION AND IMMUNITY 



treated subjects. His experiments and those of his pupils were con- 

 ducted with a large variety of microorganisms, among which were the 

 typhoid and dysentery bacilli, the bacUli of chicken cholera and of plague, 

 the cholera spirillum, and various micrococci. According to whether a 

 microorganism is capable o'f producing an aggressin and consequently 

 of invading the animal body, he divides bacteria into "pure parasites," 

 "half parasites," and "saprophytes." 



The theory of Bail has been extensively attacked by a number of 

 authors, chief among whom are Wassermann and Citron,' Wolff, ^ and 

 Sauerbeck.^ The criticism which these investigators make of Bail's 

 views is based upon laborious experimentation and has succeeded in 

 placing' the "aggressin" theory upon a very precarious footing. It is 

 claimed by them, in the first place, that much of the "aggressive" 

 character of Bail's exudates is due to their containing liberated bacterial 

 poisons (endotoxins). This they have maintained both because the 

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

 degree of independent toxicity and because the aggressive action of such 

 an exudate could be duplicated by aqueous extracts of bacteria. Citron,* 

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

 plement fixation, that the exudates of Bail contained considerable 

 quantities of free bacterial receptors, which, in taking up bacteriolytic 

 immune body, would neutralize any lytic power on the part of the in- 

 fected animal. By this antilytic action, he believes. Bail's first conten- 

 tion, the virulence-enhancing action of the exudates, can be explained. 

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

 treatment is less easily explained and less exposed to adverse criticism. 

 Bacteriolytic immunity alone probably can not account for the high 

 degree of resistance imparted by a few injections of the aggressins. 

 On the other hand, the establishment of an antiaggressive immunity 

 has not been sufficiently supported to stand as a proven fact. Final 

 judgment must be postponed until further investigation shall have 

 brought a better understanding of the phenomenon. 



' Wassermann and Citron, Deut. med. Woch., xxviii, 1905. 



2 Wolff, Cent. f. Bakt., I, xxxviii, 1906. 



^Sauerbeck, Zeit. f. Hyg., Ivi, 1907. 



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



