SOME COMMUNICABLE DISEASES 355 



the gas produced by the blackleg germs in the tissues. The 

 tumor is cool to the touch, non-sensitive, and is found to contain 

 a frothy, bloody fluid with a peculiar sweetish odor. Guinea 

 pig inoculation is the most reliable means of establishing a 

 diagnosis. 



Treatment. — Remedial treatment is useless. Preventive treat- 

 ment by means of a vaccine is very effective. The method of 

 vaccination most largely used consists in inoculating healthy 

 susceptible cattle with a vaccine composed of attenuated spores 

 of the blackleg organism. The losses following vaccination are 

 less than J^ of 1 per cent. 



CONTAGIOUS ABORTION 



The contagious form of abortion in cattle is a chronic, in- 

 sidious disease that confines its ravages largely to the organs 

 of reproduction. It is the most widespread of all diseases to 

 which cattle are subject. Mares also suffer from this disease to 

 such an extent that in some sections the raising of foals is 

 unprofitable. 



Cause. — A specific germ has been discovered for each animal 

 species. In cattle the abortion bacillus of Bang is the cause. 

 This microorganism seems to require fetal tissues or milk for 

 existence, so is found almost exclusively in the pregnant uterus or 

 udder. Heifers are more likely to become infected than cows 

 because they have less resistance. The bull seldom acquires 

 the disease. Recent experiments point to the cow which has 

 aborted, rather than the bull, as the chief means of spreading 

 the abortion germs. Although most cows that become infected 

 abort sooner or later, a few appear to have a tolerance for the 

 germs and calve normally. 



Symptoms. — During the early months of pregnancy no symp- 

 toms are evident. Impending abortion is indicated by swelling 

 of the udder, congestion of the external genitals, and a discharge 

 from the vagina. The fetus is born dead or so weak that it often 

 dies within a few hours (Fig. 88). Retention of the afterbirth 

 is a frequent complication. An aborting cow gives less milk than 

 she would if normal and is likely to abort in the next gestation 

 period unless given proper treatment. 



Certain animals become "carriers" of the germs, distributing 



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