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during the year with surra, so that contagion from horse to horse is
out of the question in these cases.

Beyond this, we have the fact that there is no record to be found of
surra having been imported or become enzoötic in a locality, as the result
of the introduction of animals suffering from the disease.

With this evidence before us, can we consider the disease to be
contagious, or are we to look upon animals suffering from the disease as
a source of danger to healthy animals? The answer appears to be in the
negative, and we are led to the opinion that surra is what, might be
called an "accidental" disease of the horse, introduced from without,
owing to the animal ingesting the infusorian; and not contagious in the
ordinary acceptation of the term, but only under certain conditions.

The disease can be transmitted from a sick to a healthy animal, (i) by
subcutaneous inoculation with blood, whether it be taken during a
paroxysm or intermission serum, fluid taken from the tunica vaginalis,
the pericardial sac, and lateral ventricles. (ii) By the gastric inges-
tion of such blood. (iii) By direct injection into the general circulation.

Blood taken some hours post-mortem, and from which the infusorian
has apparently disappeared, will also induce surra on inoculation.

Experiments are necessary to show for what length of time the blood
remains virulent after death.

Period of Incubation.—It is impossible to say presisely what the
period of incubation in naturally-contracted cases of surra may be, but
it is probably between 39 and 67 days.

In cases induced by the subcutaneous inoculation of blood taken
during a paroxysm, we find it to be usually from four to seven days, and
it is about the same when the infusorian is injected directly into the
general circulation.

If the blood be taken from the heart or great vessels some hours
after death (5 to 16 hours), we find the period of incubation lasting from
8 to 13 days. We find that there is some increase in the length of the
period here; and it appears that some change occurs after death which
delays the process; for, with blood taken only an hour and a half after
death, the incubative period was only 6 days. Cases due to gastric in-
gestion of large quantities of blood containing the infusorian have an
incubative period of 5 or 6 days, but if the quantity of blood be small
it is very long and variable.

Animals susceptible to Surra.—Horse Surra may be transmitted by
inoculation to the donkey mule, ox, sheep, goat, monkey, dog, cat, rabbit,
guinea-pig, and rat.

In the donkey and mule, it runs a course similar to that in horses,
but it is usually slower, taking much longer to kill them. In the dog,