474 PATHOGENIC MICROORGANISMS 



64 per cent of hydrogen, 28 per cent of COj, and 8 per cent of a mix- 

 ture of gases, chiefly nitrogen. The gas from the infected animal body 

 is ignitable and burns with a bluish hydrogen flame. 



Biological Considerations. — The bacillus, as stated, is anaerobic. Its 

 anaerobic requirements, however, are less exacting than those of some 

 other anaerobes, and in stab cultures it will often grow up to the surface 

 of the stab. It grows best at 37.5° C, but will also develop at room 

 temperature (20° to 22° C). 



Isolation. — The bacillus may, of course, be isolated by anaerobic 

 plating methods. It is best isolated, however, from mixed cultures by 

 animal inoculation. If, for instance, it is desired to obtain it from a 

 mixed culture or from feces, a suspension of about 1 c.c. of the 

 suspected material is made in 5 c.c. of sterile salt solution. This 

 is thoroughly emulsified and filtered through a sterile paper. One 

 to two c.c. of this suspension is then injected into the ear vein 

 of a rabbit.- After four or five minutes the rabbit is killed. It 

 is then placed in the incubator for five to eight hours. At the 

 end of this time, the animal is usually found tensely distended with 

 gas. At autopsy, gas bubbles will be found distributed through- 

 out the organs, most characteristically in the liver, where isolated 

 bubbles are found covering the surface. From these bubbles cul- 

 tures or smears may be taken for identification. Identification is 

 easily made from its morphology, its capsule, lack of motility, and 

 gas formation. 



Pathogenicity. — Bacillus aerogenes capsulatus is highly pathogenic 

 for guinea-pigs, but very slightly for rabbits. Its virulence is subject 

 to great variations, however, some strains showing little if any pathogen- 

 icity even for guinea-pigs. In general, its pathogenicity for the ordi- 

 nary laboratory animals may be regarded as slight. In man,* the 

 bacillus has been isolated from numerous cases of so-called "emphyse- 

 matous gangrene"^ (gangrene foudroyant). The infection usually 

 occurs upon the extremities and is characterized by a rapidly necro- 

 tizing inflammation, with which there occurs extensive subcutaneous 

 emphysema. The infection usually follows traumatism,^ especially 

 compound fractures, and is extremely grave. The bacillus has also 

 been found in the uterus in puerperal infection,* and in. the fetus 



' Welch and Flexner, Jour. Exp. Med., 1, 1896. 



'Mann, Ann. of Surgery, xix, 1894. 



' Bloodgood, Progressive Med., 1899. 



» Pobbin, Johns Hopkins Hosp. Bull., viii, 1897. 



