ARTIFICIAL AGGRESSINS 45 



and cholera toxin) are capable of producing a fatal effect when 

 injected together with subfatal doses of bacteria. 



It is also quite clear now why the simultaneous injection of cer- 

 tain bacilli together with suitable quantities of aggressin exudate 

 and corresponding bactericidal (bacteriolytic) serum does not lead 

 to the destruction of the bacteria. Bail assumed an antagonistic 

 action upon the bactericidal substances on the part of his hypo- 

 thetical aggressins, while the same effect or rather lack of effect is 

 now explained as the consequence of a neutralizing or inhibiting 

 effect of normal bacterial disintegration products (receptors) upon 

 the bacteriolysins. As suitable treatment of animals with bacterial 

 extracts and killed cultures of bacteria leads to the production of 

 a certain type of immunity, in which antitoxins and certain bacteri- 

 cidal substances (bacteriolysins) play a prominent role, and as we 

 have seen that bodies of that order (bacillary proteins and toxins) 

 can actually be demonstrated in the aggressin exudates, it follows 

 that there is no ground for the assumption that an antiaggres'sin 

 immunity as an immunity sui generis exists. 



A final point which has been raised against Bail's theory is the 

 fact that in the antiaggressin immune animal (in the sense of Bail) 

 there is no evidence either of increased phagocytic activity or of 

 increased resistance to the multiplication of bacteria. Weil, one 

 of Bail's pupils, has thus shown in chicken cholera infection, for 

 example, that the increase of bacilli in the immune animal may be 

 just as intense as in the control animal two hours before death, while 

 the virulence, as tested on non-immune animals, is unimpaired, and 

 there is no evidence of phagocytosis. While Bail's whole theory 

 of antiaggressin immunity has thus fallen to the ground it must be 

 admitted that in the truly infectious (septicemic) diseases, bacterio- 

 lytic immunity likewise does not play a role, and the question hence 

 still remains an open one; how to account for the undoubted im- 

 munity which can be produced by repeated injection of animals 

 with so-called aggressins. As the protection of animals, which is 

 thus obtained, is not transferable, i. e., as one animal cannot be ren- 

 dered resistant (immune) by the injection of blood from an aggressin- 

 immune animal, the question naturally suggests itself, whether, 

 after all, we are not dealing with a type of immunity which is different 

 from the other forms that are commonly recognized. This question 

 will be discussed at greater length in a later chapter; suffice it to say 



