LEUCOCIDIN. 539 



lytic action of the staphylococcus is readily seen 

 in cultures on blood-agar plates; a zone of hemo- 

 lysis forms about the colonies. Erythrocytes of the 

 rabbit, when placed in bouillon cultures, undergo 

 hemolysis. Staphylotoxin also produces hemolysis 

 in the living body. The maximum production of 

 staphylolysin occurs after a growth of nine to 

 fourteen days in alkaline bouillon, and nearly 

 all pathogenic strains yield it, whether aureus, 

 albus or citreus. It is not formed by non-patho- 

 genic strains. The toxin is destroyed by exposure 

 to a temperature of 56 C. for twenty minutes. A 

 specific antitoxin is present in many normal 

 serums and may be increased by immunization 

 with the toxin or the living organisms. 



In 1894 van der Velde found in the pleural 

 exudates caused by inoculation with killed cultures 

 of the staphylococcus a substance which is toxic 

 for leucocytes, causing them to swell and the nuclei 

 to disappear. This substance is called leucocidin. 

 It is also produced in culture media, but the ability 

 to form it is not so widely distributed as in the 

 case of the hemolysin. Leucocidin is a true toxin, 

 like the hemolysin; most normal serums contain 

 antileucocidin, and the latter is increased by im- 

 munization with the toxin. 2 The suggestion is a 

 natural one that leucocidin may be a factor in 

 combating phagocytosis in infections with the 

 etaphylococcus. Neisser and Wechsberg de- 

 vised a "bioscopic method" of determining the 

 cytocidal action of the toxin. Living leucocytes, 

 like other living cells, have the power of decoloriz- 

 ing methylene blue when oxygen is excluded. The 



2. Leucocidin and staphylolysin will not yield antitoxins 

 when their activity has been destroyed by heat. 



