anding of the methods of prevention. Many
investigators have demonstrated that the infection is transmitted through
the digestive tract, through contaminated feed and water. The germs are
taken up by the body from the intestines with the liquid nourishment, reach
the blood, and are carried to the genital organs, where they find
conditions best suited to their development. Some assert that calves are
infected in this manner by suckling infected mothers, the germs being
present in the milk, or the teats having been contaminated by coming in
contact with infective discharges. It is claimed that infection contracted
in this manner remains dormant in the body of the calf until pregnancy
begins, and then the organism, finding conditions suitable for its
development, produces the disease.

Abortion may occasionally be transmitted from cow to cow by direct contact.
The discharges from diseased cows, swarming with the germs, soil the
external genitals, tail, and hind quarters, and then a susceptible animal,
by contact, gets the infective material upon the vulva, the infection
traveling up the genital canal and directly infecting the uterus.

The belief long entertained that the female acquires the disease at the
time of copulation as a result of transference of the infection from
affected to healthy females on the genital organs of the bull has failed to
receive the support of experimental evidence. The view that the disease is
spread to any great degree in this way has been largely discredited. Cows
of all ages are more or less susceptible, but young ones in first or second
pregnancy most frequently abort. A second abortion is not unusual, and a
third may occasionally occur, after which the cow usually becomes immune
and thereafter carries her calf to maturity. Heifers from aborting mothers
sometimes seem to be less susceptible than others.

_Symptoms._--Contagious abortion is a very insidious disease, developing
very slowly through several months of the gestation period, and resulting
finally in the expulsion of the immature young, this act being simply an
indication of the presence of the disease and not the disease itself.
Because of this slow development and the fact that the health of the animal
is not noticeably influenced, the presence of the disease may not be
suspected until it has gained a firm foothold in the herd. The symptoms of
approaching abortion are those preceding normal calving. In addition, there
may be obs