oductive organs.

The contagious nature of the disease had not been recognized until
recently, the disease being principally attributed to various
conditions, such as traumatic influences, various infectious diseases,
spoiled feed, drugs, and other factors. Ostertag was the first to study
premature births in mares, attributing as the cause of the same a
streptococcus, which he was supposed to have been able to use
successfully in artificially producing abortion, either by inoculations
or feeding. His findings could not be substantiated by other
investigators.

The earliest appearance of the disease in this country was in 1886, at
which time it caused considerable damage to the horse-breeding industry
in the Mississippi Valley. Smith and Kilbourne investigated an outbreak
in Pennsylvania in 1893, at which time they incriminated another germ
belonging to the paratyphus B group as the causative factor of the
disease. These findings have been subsequently substantiated by many
investigators abroad, as well as in this country, notably so by De Jong,
Dassonville, and Riviere, and by Good and Meyer. More recently very
valuable information was contributed to our knowledge on this disease by
Schofield, of Canada, especially with regard to the biological tests for
diagnosis. Good suggested "_Bacillus abortivus equinus_" as the name for
the specific organism.

The causative agent of this disease is not identical with the germ
causing abortion in cattle. It exerts its action, however, in a similar
manner, and appears to have, under certain conditions, a predilection
for the genital organs of the mare, where it induces certain morbid
changes whereby a premature expulsion of the fetus is the result. The
germ is usually present in the fetal membranes and also in the aborted
fetus. Mares may harbor the infection without disclosing any apparent
ill effects. It appears to exert its influence mainly upon the female
genital organs, where it may induce an inflammatory condition of the
uterus.

The infected animals may carry the fetus through the normal period of
pregnancy, giving birth to either a normal or a weak colt, or again
abortion may take place at any time during pregnancy, mostly, however,
from the sixth to the ninth month.

_Symptoms._--The symptoms suggestive of abortion are frequently entirely
absent. At times the abortion may be ushered in by symptoms of colicky
pains, restlessness, and periodical straining; these, howeve