oes not
invariably follow infection, but the calf is carried to full term. In these
cases, however, retained afterbirth is a common occurrence, even to the
extent that frequent retention of afterbirth in a herd may be taken as an
indication of the presence of the disease. Very often suppurative processes
persist for a long time, preventing conception, or sterility may result
without apparent cause. A sterile cow is valueless, of course, for any
purpose except for beef. Such animals are a source of infection for the
others and should not be allowed to remain in the herd.

_Diagnosis._--The diagnosis of infectious abortion is made from the changes
occurring in the fetal membranes and in the expelled fetus. This, however,
is substantiated with certainty only by microscopic demonstration of the
germ of abortion. The fact that repeated abortions are observed in a herd
is also evidence of the presence of the disease. In consideration, however,
of the fact that animals may be affected with the disease and disseminate
the germs, even though they carry the fetus to full time, a diagnosis in
such instances is only possible by laboratory methods. For this purpose the
agglutination and also the complement-fixation tests are being used with
splendid results, and by the aid of these biological tests it is possible
to determine all infected animals in a herd. The tests are carried out with
the serum from animals to be examined, only a teaspoonful of serum being
necessary for the execution of both of these tests. It, however, has to be
confined to laboratories which are properly equipped for such work.

_Treatment and prevention._--It may be said in general that treatment is
without avail and all efforts should be directed toward prevention. Various
medicinal agents, such as carbolic acid administered subcutaneously and
methylene blue fed in large quantities, have been recommended, but have
failed to stand the tests of scientific investigation and practical use.
Serums and vaccines have also been prepared and sold as cures and
preventives, but the work is still considered in the experimental stage.

Bacterial vaccines are at present extensively used in the control of this
disease, and while numerous reports indicate beneficial results from their
administration, in other instances total failures have been recorded. It
appears that the experiments in this line have not progressed sufficiently
to justify definite conclusions.

The sprea