STAPHYLOCOCCUS PYOGENES AUREUS 395 



by the simple method of Van de Velde, of injecting virulent staphylo- 

 cocci intrapleurally into rabbits and examining the exudate. Bail 

 advises the production of leucocytic intrapleural exudates by the use 

 of aleuronat and following this after twenty-four hours by an injection 

 of leucocidin-filtrate. In vitro the phenomenon may be observed by 

 direct examination of mixtures of leucocytes and leucocidin in the 

 hanging drop on a warmed stage, or by the t ' methylene-blue 

 method" of Neisser and Wechsberg. This method is based upon the 

 fact that living leucocytes will reduce methylene-blue solutions and 

 render them colorless, while dead leucocytes have lost this power. 

 Leucocidin and leucocytes are allowed to remain in contact for a 

 given time and to them is then added dilute solution of methylene- 

 blue. If the leucocytes have been actively attacked by leucocidin, 

 no reduction takes place. This method is particularly adapted for 

 quantitative tests. 



All staphylococcus strains do not produce leucocidin to the same 

 degree. Almost all true Staphylococcus pyogenes aureus cultures 

 produce some of this taxin, but one strain may produce fifty- and a 

 hundred-fold the quantity produced by another. Staphylococcus 

 pyogenes albus gives rise to this substance but rarely, and then in 

 small quantity. 



Leucocidin seems to be similar to the soluble toxins of other 

 bacteria. It is rapidly destroyed by heat at 58 C., and deteriorates 

 quickly in culture fluids at incubator temperatures. It is distinct 

 from staphylohemolysin as shown by differences in thermostability. 



Soon after Van de Velde 's discovery of leucocidin, Denys and 

 Van de Velde 32 produced an antileucocidin by treating rabbits with 

 pleural exudate containing leucocidin. Neisser and Wechsberg 33 

 later confirmed these results and showed that among staphylococci, 

 leucocidin is not specific, the toxin of all strains of Staphylococcus 

 aureus and albus examined being neutralizable by the same anti- 

 leucocidin. Antileucocidin is often found in the normal sera of 

 horses and man. 34 



Leucocidin should not be confounded with "leucotoxin," a sub- 

 stance obtained in serum by treatment of animals with leucocytes, 

 a true "cytotoxin," having no connection whatever with the staphy- 

 lococcus. 



32 Denys et Van de Velde, La Cellule, xi, 1895. 



33 Loc. cit. 



34 Van de Velde, Presse medicale, i, 1900. 



