EXPERIMENTAL INOCULATION 447 



in a certain proportion of cases. Instances have also been 

 recorded in which they have settled in other parts of the 

 body and produced lesions there — the so-called metastatic gas 

 gangrene. 



Experimental Inoculation. — The virulence of the b. welchii 

 varies considerably. Some strains when injected into a guinea- 

 pig, even in considerable doses, cause only some inflammatory 

 swelling which passes off; especially is this the case when an 

 emulsion of the bacilli from a surface culture is used. Other 

 strains, again, produce a fatal result, even in small doses ; there 

 occurs at the site of injection an inflammatory oedema with 

 blood-stained fluid and some evolution of gas, and a certain 

 amount of necrosis of the underlying muscle. Bacilli are 

 abundant locally, but only a few are present in the blood stream. 

 When the dose is sublethal a local gangrene may occur, with 

 subsequent separation of the dead tissue ; thereafter healing may 

 rapidly follow. Intramuscular injection is the most effective 

 method, especially in the rabbit, which is more resistant than the 

 guinea-pig. The pigeon is found to be the most susceptible of 

 the animals hitherto tested, the lethal dose being only a fraction 

 of that for the guinea-pig. Injection into the pectoral muscle of 

 a pigeon causes lesions in the muscle closely resembling those in 

 gas gangrene in man, and death follows very rapidly, sometimes 

 within a few hours. Most observers have found filtered cultures 

 to be practically non-toxic, but recently Bull and Pritchett have 

 succeeded in obtaining a true exotoxin. The medium used by 

 them was plain meat bouillon containing fragments of sterile 

 skeletal muscle of the pigeon or rabbit. After inoculation the 

 medium is incubated under anaerobic conditions at 37° 0. for 

 twenty-four hours, and is then filtered through a Berkefeld N 

 candle. The filtrate was found to be highly toxic for all the animals 

 mentioned above, and gave rise to local lesions closely resembling 

 those caused by the bacilli themselves. In addition to having a 

 local necrotic effect on muscle, the toxin, or a moiety of it, is 

 actively haemolytic, and leads to a massive destruction of red 

 corpuscles when injected intravenously. Bull and Pritchett 

 believe, accordingly, that death from gas gangrene is due to a 

 true toxaemia and not to the production of acid in the tissues as 

 has been supposed by some. By means of injecting carefully 

 graduated doses of the toxin, they have produced an active 

 immunity, and the serum of the treated animals possesses anti- 

 toxic properties. The antitoxin neutralises all the effects of the 

 toxin in multiple proportions, and is protective and curative 

 against infection with the bacillus in the pigeon. The applica- 



