326 KWlKE PBACflCE 



The B. edeliiatis uialigiii varies iu length from 2 to 4 microns, 

 although the filaments in culture media may become 15 microns in 

 length. These microorganisms average about one micron in diameter. 

 They are freely motile and stain readily with the ordinary aniline 

 dyes. Spore formation causes a slight bulging of the bacillary walls. 

 The spores are very resistant to external influences. 



These organisms are strictly anaerobic. They grow at room temper- 

 ature on any ordinary culture medium. Gelatine is liquefied and stal) 

 cultures in agar show development of gas. 



Predisposing causes are of prime importance in the occurrence of 

 malignant edema in swine. The injury incidental to the injection of 

 serum or virus in the simultaneous immunization provides a favorable 

 field for the development of the bacilli which may be introduced witli 

 the serum of virus but are more frequently carried into the tissues 

 by the needle from the contaminated skin or may gain access through 

 the needle puncture. Insanitary pens, lots and sheds favor the de- 

 velopment of malignant edema in swine. Swine that are filthy or 

 muddy should not be immunized because of the danger of infection of 

 the needle puncture with the bacillus of malignant edema. 



Operative wounds incidental to castration, scrotal hernia, ablation 

 of mammary glands and cesarean section should be properly protected 

 as the surrounding tissues have a diminished resistance due to the 

 operative procedure, otherwise infection and the development of malig- 

 nant edema may occur. The ringing or ear-marking of swine also 

 provides a favorable field for infection. Parturition is an important 

 predisposing factor and it is probable that many of the cases of so- 

 called septic metritis are malignant edema. 



Source of infection. — Infection with the B. edematis maligni is 

 obtained most frequently from soil or fecal discharges. Serum or 

 virus may be contaminated at the biologic establishment producing it, 

 but is more frequently contaminated in the field by dust gaining 

 access to the serum or virus containers. Some outbreaks of malignant 

 edema have been traced to syringes that have not been sterilized 

 previous to use. In many instances the recently immunized or 

 castrated swine have not been placed and maintained in clean quarters 

 by the owners, as instructed by the veterinarian and the needle punc- 

 tures or operative wounds have become contaminated and infection 

 with the B. edamitis maligni resulted. 



Channels of entrance of infection. — Malignant edema is practically 



