196 THE TOXINS PRODUCED BY BACTERIA 



cellular toxin. As evidence of the existence of a special group 

 of toxins, it has been stated that a special type of immunity 

 against the aggressins can be originated. Perhaps the most 

 important aspect of the controversy is the recognition of the 

 existence of toxins having an action on the leucocytes. A poison 

 causing death of these cells in connection with the pus-forming 

 action of the pyogenic cocci has been described under the name 

 of leucocidiii, and Eisenberg records that in in vitro mixtures of 

 leucocytes and cultures of the bacillus of symptomatic anthrax 

 loss of motility and degeneration of the cells may be observed. 



Sometimes the media in which bacteria are growing become 

 extremely toxic. This is more marked in some cases than in 

 others. The two best examples of bacteria thus producing 

 soluble toxins are the diphtheria and tetanus bacilli. In these 

 and similar cases when bouillon cultures are filtered bacterium- 

 free by means of a porcelain filter, toxic fluids are obtained, 

 which on injection into animals reproduce the highly character- 

 istic symptoms of the corresponding diseases. In the case of 

 the b. anthracis and of many others, at any rate when growing 

 in artificial media, such toxin production is much less marked, 

 a filtered bouillon culture being often non-toxic. Poisons ap- 

 pearing in culture media have been called extracellular toxins, 

 but we cannot as yet say whether they are excreted by the 

 bacteria or whether they are produced by the bacteria acting on 

 the constituents of the media. The extracellular toxins are 

 easily obtainable in large quantities, and it is their nature and 

 effects which are best known. No method has been discovered 

 of obtaining them in a pure form, and our knowledge of their 

 properties is exclusively derived from the study of the toxic 

 filtrates of bouillon cultures these filtrates being usually re- 

 ferred to simply as the toxins. These toxins differ in their 

 effects from the intracellular poisons in that specific actions on 

 certain tissues are often manifested. Thus the toxins of the 

 diphtheria, the tetanus, and the botulismus bacilli all act on 

 the nervous system ; with some of the pyogenic bacteria, on the 

 other hand, poisons, probably of similar nature, produce solution 

 of red blood corpuscles (this last might be thought to explain 

 the anaemias so common in the associated diseases, but here 

 further work is still necessary). In the action of many of these 

 toxins the occurrence of a period of incubation between the 

 introduction of the poison into the animal tissues and the ap- 

 pearance of symptoms is often a feature. 



The whole question of the parts played by toxins in bacterial 

 action is manifestly very complex. On the one hand, we have 



