TUBERCULOSIS. * 231

individual, so that, a short time after its enthusiastic
reception as a "gift of the gods," tuberculin was placed
upon its proper footing as a diagnostic agent valuable in
veterinary practice, but dangerous in human medicine,
except in cases of lupus and other external forms of the
disease where the destroyed tissue could be discharged
from the surface of the body.

The method of preparation of tuberculin is rather
simple. Small flasks exposing a considerable surface of
liquid are filled with about 25 c.cm. of bouillon contain-
ing about 4 per cent, of glycerin. The bouillon is prefer-
ably made with calf- instead of ox-meat. When thor-
oughly sterile the surfaces are inoculated with pure
cultures of the tubercle bacillus and are stood in an
incubator. In the course of two weeks a slight surface
growth is apparent, which in the course of time develops
into a pretty firm pellicle and gradually subsides. At the
end of four or six weeks development ceases and the
pellicle sinks. The contents of a number of flasks are
then collected in an appropriate vessel and evaporated
over a water-bath to one-tenth their volume, then filtered
through a Pasteur-Chamberland filter. This is crude
tuberculin.

When such a product is injected in doses of a fraction
of a cubic centimeter an inflammatory and febrile reac-
tion occurs. The inflammation sometimes causes super-
ficial tuberculous lesions (lupus) to ulcerate and slough
away, and for this reason is of some value in therapeutics,
although attended with the dangers mentioned above.
The fever is sufficiently characteristic to be of diagnostic
value, though the tuberculin can only be used as a diag-
nostic agent in practice upon animals.

A recent important work upon tuberculin has been
done by Koch.1

In his experience the attempts made to produce im-
munity to the tubercle bacillus by the injection into
animals of attenuated cultures proved failures, because

1 Deutsche med. Wochenschrift^ 1897, No. 14.