42 OFFENSIVE FORCES OF THE INVADING MICROORGANISM 



the destruction of the bacteria. Bail assumed an antagonistic action 

 upon the bactericidal substances on the part of his hypothetical 

 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 

 bactericidal 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 anti- 

 aggressin 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 rendered 

 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 Chapter IX; suffice it to say at 

 this place that there is evidence to show that this type of immunity 

 is essentially an antitoxic immunity, but one in which the antitoxic 

 effect is probably the outcome of structural changes in the chemical 

 make-up of the cell and not the result of a liberation of antitoxic 



