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.