2Q2 THE AGGRESSINS 



cells of which had not taken up any bacteria, were collected, and 

 were found to have a most potent effect in increasing the lethal 

 action of the organism. This could not be tested on rabbits, 

 since they were loo susceptible, but in guinea-pigs it was found 

 to lower considerably the lethal dose. A most interesting obser- 

 vation was made : A guinea-pig which had received a small dose 

 of a culture of chicken cholera, and had apparently recovered 

 completely, was injected eight days after with some of the exudate, 

 and died of chicken cholera septicaemia, showing that the bacteria 

 were but latent, and had been allowed to become virulent and 

 active in virtue of the action of the exudate. Further, this fluid, 

 when injected into rabbits, was found to immunize them against 

 subsequent injections of the organism, even if mixed with the 

 exudate, and so rendered more virulent. 



To these substances Bail gave the name of aggressins, and 

 considered them to be an entirely new type of specific substances 

 formed by the organism, and having the power of raising its 

 apparent virulence by checking phagocytosis and allowing the 

 invading microbe to flourish without hindrance : thus, by means 

 of the concurrent presence of its specific aggressin, an almost in- 

 nocuous organism, such as B. subtilis, becomes extremely virulent. 

 According to Bail and his followers, aggressins are only formed in 

 vivo ; but this is denied by others, who claim that a watery emulsion 

 of certain bacteria has many at least of their peculiar characters. 



Immunity due to the injection of aggressin is supposed to depend 

 on the formation of a specific antibody, or anti-aggressin. It is 

 produced very rapidly after the injection of the aggressin, and lasts 

 several weeks or more, and is supposed to be due to the immediate 

 neutralization of any aggressin which the bacterium may form in 

 vivo by the anti-aggressin, so that phagocytosis in unchecked. 



Agressins are sharply specific, except perhaps in the case of 

 those for B. typhosis and B. coli i.e., the injection of one aggressin 

 will not prevent the phagocytosis of any species of bacterium 

 other than that by the action of which it was prepared ; hence 

 they are not mere leucocyte poisons : they are thermolabile. 



A substance which prevents phagocytosis may act on the leuco- 

 cyte, the bacterium, or on the serum. The fact just described 

 (that phagocytosis of a bacterium A can go on in the presence of 

 an aggressin B) shows that the action of the aggressins is not on 

 the leucocytes. Further, as Weil and Nikayama have shown, 

 bacteria which have been acted on by their aggressins and the 



