190 THE TOXINS PEODUCED BY BACTERIA 



produced by aggressins are attributed to a paralysing action 

 on the phagocytic functions of the leucocytes. The subject is 

 full of difficulties, and in the case of certain of the organisms 

 employed it is stated that results similar to those attributed to 

 aggressin action have been observed with macerated cultures, 

 the deduction being that in the aggressins we are merely dealing 

 with concentrated intracellular toxins. On the other hand, 

 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' 

 leucocidin, and Eisenberg records that in in vitro mixtures of 

 leucocytes and cultures of the bacillus of symptomatic anthrax 

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

 The investigation of such poisons must be of the highest 

 importance in view of the part played by the blood-cells in the 

 protection of the body against infection, and it is possible that 

 toxins having a fatal effect in strong concentrations may, when 

 dilute, be responsible for the phenomena of attraction or repulsion 

 of leucocytes which we know occur round a focus of bacterial 

 growth in the body. 



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 relatively non-toxic. Poisons 

 appearing 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 

 nitrates of bouillon cultures these filtrates being usually re- 



