the appearance of the first symptom.

_Anatomy._--If animals which have succumbed to rabies are examined post
mortem, very slight evidence of disease will be found in any of the organs,
and, indeed, the absence of any specific lesions may be considered as
characteristic. The blood is dark and imperfectly coagulated. The throat is
frequently reddened, and there may be small spots of extravasated blood in
the intestines. The stomachs are usually empty. In the spleen there may be
hemorrhagic enlargements (infarcts). The cadavers rapidly undergo
decomposition.

_Differential diagnosis._--It is not an easy matter to decide definitely
that a given animal has rabies, since the symptoms given above belong in
part to a variety of other diseases, among which may be mentioned the
excitement seen in young animals following close confinement, certain
vegetable and mineral poisons, acute enteritis, and alterations of the
central nervous system in cattle, the most common of which is tuberculosis
of the brain and its covering membranes. The post-mortem lesions, however,
should assist in making a correct diagnosis. Tetanus may readily be
differentiated from rabies by the persistence of muscular cramps,
especially of the face and abdomen, which cause these muscles to become set
and as hard as wood. In tetanus there is also an absence of a depraved
appetite or of a willful propensity to hurt other animals or to damage the
surroundings. The cow remains quiet and the general muscular contraction
gives her a rigid appearance. There is an absence of paralysis which marks
the advanced stage of rabies. The form of dumb rabies in dogs is
characterized by the paralysis and pendency of the lower jaw, while in
tetanus the jaws are locked. This locking of the jaws in cattle renders the
animal incapable of bellowing, as in rabies. Finally, tetanus may be
distinguished from rabies by the fact that the central nervous system does
not contain the infectious principle, while in rabies the inoculation of
test rabbits with the brain or cord of a rabid animal will produce the
disease with characteristic symptoms after an interval of 15 to 20 days.
This period of incubation is much longer than in tetanus, since the
inoculation of rabbits with tetanus cultures invariably results in death
after a short period and usually within three days. The positive evidence
that a rabid dog has been near cattle would greatly assist in making a
decision in doubtful cases.