LEUCOCIDIN. 121 



was applied to the bactericidal substances of the 

 serum. Their existence had no satisfactory sup- 

 port at that time. 



A little later van der Velde discovered that 

 staphylococci secrete a substance which is toxic for 

 leucocytes, the so-called leucocidin. It appeared to 

 be produced by strains of both high and low viru- 

 lence. Still more recently it was discovered that 

 the streptococcus produces a toxin which is 

 destructive for leucocytes (Kuediger, Besredka). 

 These results suggest that a toxic action on the 

 leucocytes may be a factor for the progress of 

 infection,, and may explain, at least in part, the 

 resistance which virulent organisms show toward 

 phagocytosis. A particularly significant observa- 

 tion is that by Kosenow, to the effect that virulent 

 pneumococci secrete a substance which has the 

 power of inhibiting phagocytosis, a substance to 

 which the name of virulin was given. Virulin can V i ril ii 

 be extracted from virulent cultures by means of 

 salt solution, and after this has taken place the 

 cocci have become susceptible to phagocytosis. Also 

 after avirulent strains have been treated with the 

 extracted virulin, and later separated from it by 

 washing, they are found to have acquired resist- 

 ance to phagocytosis. Eisenberg also observed that 

 leucotoxic substances are produced by the bacilli of 

 symptomatic anthrax and malignant edema. He 

 furthermore believes that it is a more or less com- 

 mon property of bacteria to produce such sub- 

 stances in the course of infection, although they 

 may not be obtained under artificial conditions, 

 and that they are identical with the "aggressins" 

 of Bail. The correctness of this belief, however, 

 is not fully demonstrated. 



