34 QUATERCENTENARY STUDIES IN PATHOLOGY 



The first work in this direction was done by Denys and Van de Veldc 

 (1895) who showed that a substance " leucocidine," highly toxic for 

 leucocytes, could be obtained in the pleural exudates resulting from the 

 injection of staphylococci into the pleural cavity of the rabbit, and that 

 the serum of rabbits immunised against staphylococci contained a 

 substance " anti-leucocidine," capable of neutralising the toxic action of 

 leucocidine. The leucocidine could be demonstrated to be present in 

 cultures though not so abundantly as in the exudates. 



The whole subject of the toxic and immunising action of the body 

 fluids of infected animals has been re-opened by the investigations of Bail 

 and his co-workers. This work embraces a theory of the method of 

 attack on the animal body by certain groups of bacilli, and of the nature 

 of the defence by means of which immunity is attained. Bail's views 

 may be briefly stated as follows : — Certain organisms obtain a footing in 

 the animal body by means of substances which they throw off, and to 

 which Bail gives the name of " aggressins." These are demonstrable in 

 the bacterial-free body-fluids, exudates, etc., of the infected animal. 



The aggressive property of such fluids can be shown in the following 

 manner. A non-lethal dose of the bacillus becomes lethal when mixed 

 with its specific aggressin. The presence of aggressin, along with a 

 lethal dose, causes the occurrence of a disease of a severer and more 

 acute type, and one in which the pathological lesions are of a more 

 pronounced character. 



It is, in the case of the strictly parasitic bacilli, such as anthrax, 

 fowl-cholera and plague, where a single virulent organism is probably 

 sufficient to cause infection, that the aggressin action is most marked. 

 The living bacillus can, without losing its vitality, secrete or throw off* 

 particles which prevent its destruction by phagocytes, and enable it, 

 at the same time, to multiply and produce its pathogenic effects. 



The immunity obtained by the injection into the animal body of 

 natural aggressins is attributed by Bail to the production of anti- 

 aggressins. 



Wassermann and Citron (1905) hold, that aggressins can be obtained 

 outside the animal body by shaking bacteria in serum or in distilled 

 water. The fluids obtained by these means, after removal of the living 

 germs, are capable of aiding the infective process. Their view is, that 

 the aggressins, whether obtained from the animal body or by this method, 



(144) 



