latively few failures in
diagnoses are included among two classes of cattle. The first class
contains those that are tuberculous, but which do not react either because
of the slight effect of an ordinary-sized dose of tuberculin on an advanced
case of the disease with so much natural tuberculin already in the system,
or on account of a recent previous test with tuberculin which produces a
tolerance to this material, lasting for about six weeks. The second class
includes those that are not tuberculous, but which show indications of a
reaction as a result of (_a_) advanced pregnancy, (_b_) the excitement of
[oe]strum, (_c_) concurrent diseases, as inflammation of the lungs,
intestines, uterus, udder, or other parts, abortion, retention of
afterbirth, indigestion, etc., (_d_) inclosure in a hot, stuffy stable,
especially in summer, or exposure to cold drafts or rains, (_e_) any change
in the method of feeding, watering, or stabling of the animal during the
test. Notwithstanding all these possibilities of error, the results of
thousands of tests show that in less than 3 per cent of the cases tested do
these failures actually occur. In the first class the chances of error are
decidedly reduced by the skilled veterinarian by making careful physical
examination and diagnosing clinically these advanced cases, and by the
injection of double or triple doses into all recently tested cattle, with
the taking of the after-temperature, beginning two hours following the
injection and continuing hourly for 20 hours.

It is therefore apparent that tuberculin should be applied only by or under
the direction of a competent veterinarian, capable not only of injecting
the tuberculin but also of interpreting the results, and particularly of
picking out all clinical cases by physical examination. The latter
observation is extremely important and should always be made on every
animal tested.

In the second class, where the temperature test is used, errors are avoided
by eliminating from the test those cases that are nearing parturition or
are in heat or show evidence of the previously mentioned diseases or
exhibit temperatures sufficiently high to make them unreliable for use as
normal. Where other methods of test are used these conditions do not have
an important bearing on the results. In addition, a satisfactory tuberculin
must be used; also an accurate thermometer and a reliable syringe, in order
that a sufficient dose of tuberculin may be