MALIGNANT EDEMA Q51 
have been described. It is possible that they are modified forms of 
the one species. 
Of the domestic animals, the horse is the most susceptible to natural 
infection; the cow, the sheep and the goat are less susceptible. The 
pig, dog and cat are rarely attacked. 
Infection sometimes follows contusions or lacerations and incis- 
ions and sometimes delivery, when help is given with hands or 
instruments not clean. It also occurs from injuries such as castra- 
tion, shearing, bleeding, drawing setons, and subcutaneous injections. 
Fic. 52. BACILLUS OEDEMATIS MALIGNI WITH FLAGELLA AND 
sPoRES (Hutyra). 
This organism produces a toxin. Besson found that if spores freed 
from the toxin were injected they were destroyed by the phagocytes 
and no lesions were obtained. 
Morbid anatomy. On the expansion of a tumor appearing in any 
part of the body, the connective tissue is distended and infiltrated 
with yellow or reddish fluid containing many small gas bubbles, which 
emits a characteristic odor. These gelatinous infiltrations of the 
connective tissue follow between the deeper layers of the muscle. 
The muscle itself is often sallow or dark red in color and is very 
brittle. The connective tissue in places is often sprinkled with larger 
or smaller hemorrhages. In the intestinal cavity there is a little 
reddish, serous fluid; the peritoneum is deeply injected. In the cases 
in which malignant edema has developed in connection with parturi- 
tion the uterus is insufficiently contracted, the subserous connective 
tissue of the true pelvis and the walls of the uterus are edematously 
infiltrated. 
The spleen is usually not affected. Occasionally acute tumors with 
gas formation are found in the pulp (Fréhner). The liver may show 
