PASSIVE AGGRESSIVITY 35 



Aggressins. Such substances Bail has termed aggressins, and he 

 speaks of aggressivity of this order as aggressivity in the narrower 

 sense, while he denotes the former as aggressivity in the wider sense of 

 the term. In their places one could substitute the terms active and 

 passive aggressivity, the latter indicating a passive resistance and the 

 former an actual offensive reaction. The general recognition of the 

 existence of a certain aggressivity on the part of the invading organ- 

 ism is most important. If in the past the attention of medical men 

 has been centred on the defensive mechanism of the invaded organism 

 this interest has been essentially a selfish one. Active progress in 

 the future, however, will depend to a considerable degree upon our 

 knowledge of the defensive forces of the invader. Our present 

 knowledge is as yet quite small, but enough has been learned to 

 establish the importance of further research in this direction. 



Passive Aggressivity. CAPSULE FORMATION. Among the passive 

 factors the most striking is the tendency to capsule formation, which 

 occurs in some of the pathogenic bacteria, while they exist in the 

 animal body, or when they are grown on media containing animal 

 albumins, such as serum, serum agar, hydrocele agar, milk, etc. 

 When the organism is transplanted to ordinary media this peculiarity 

 rapidly disappears, but can be made to reappear by transferring it 

 to albuminous media, or by reinoculation into the animal body, 

 and so on indefinitely. The most notable organisms which possess 

 this property, aside from the capsule bacteria proper, viz., those 

 organisms which even under ordinary circumstances possess a cap- 

 sule, such as the bacillus pneumonise of Friedlander, and the bacillus 

 of rhinoscleroma, are a number of streptococci (str. involutus, 

 vulvitidis vaccarum, mastitidis vaccarum, equi, mucosus), the pneu- 

 mococcus, the micrococcus tetragenus, bacterium anthracis, bacterium 

 pestis, bacterium cholerse gallinarum, certain pathogenic yeasts, etc. 

 Coincidently there seems to be an absence of that tendency to form 

 chains which is so common in the case of certain organisms, such as 

 the anthrax bacillus and certain streptococci and pneumococci, 

 when these are grown on artificial media. 



In other organisms actual capsule formation has not been observed 

 but in its place an analogous process has been noted, resulting in 

 a thickening of the ectoplasm, so that the bacteria look larger and 

 coarser. This is true especially of the colon and typhoid bacillus 

 and of the staphylococcus, and leads to appearances which often 



