VARIETIES OF TUBERCULIN AND METHODS OF PREPARATION OLD TUBERCULIN--T. Announced by Koch in 1890. Tubercle Bacilli of human origin. Grown on beef broth containing 5% glycerine, 1% peptone, sodium chloride; growths 6 to 8 weeks. Sterilized by steam one-half hour. Evaporated (at a temp. not higher than 70° C.) to 1/10 its volume. Filtered. 1/2% carbolic acid added. Let stand. Filtered (porcelain filter). Old Tuberculin contains: 1. 40 to 50% glycerine (a small percentage of glycerine is evaporated) 2. 10% of peptones or albumoses 3. Toxic secretions of the tubercle bacilli into the culture fluid, or such of them as are soluble in 50% glycerine 4. Substances extracted from the bacterial bodies by the alkaline broth during the process of boiling and evaporation. Appearance and Characteristics: 1. A clear brown fluid 2. Of syrupy consistency 3. Mixes with water in all proportions without producing any turbidity 4. Keeps indefinitely, but not advisable to use brands older than one year. BOULLION FILTRATE--B. F. Denys--1907. Method of preparation same as Old Tuberculin, with the exception of subjection to heat; B. F. is a filtered, unconcentrated culture. Contains less peptone and less glycerine than Old Tuberculin. Contains no substances extracted from tubercle bacilli by heat. Some toxic substances may be more active (not having been subjected to heat). TUBERCULIN RUCKSTAND (Residue)--T. R. Announced by Koch in 1897. Ground, dried tubercle bacilli. Distilled water added. Centrifugalization. Supernatant fluid removed (not to be used). Sediment dried and ground; distilled water added; centrifugalization. Fluid removed and _set aside_. Sediment dried and ground again; distilled water added; centrifugalization. Fluid removed and set aside. Sediment dried and ground, etc., as above. The process continued until water takes up the sediment, then all the fluids set aside (except the first one) mixed together. Glycerine 20% added. The mixture is T. R. Koch was prompted by the following consideration in bringing out T. R.: He thought that the Old Tuberculin conferred only a toxic immunity, not bacterial. T. R. was supposed to confer bacterial immunity. Each 1 cc. of T. R. contains 10 milligrams of dried bacilli. BACILLEN EMULSION--B. E. Announced by Koch in 1901. Finely powdered tubercle bacilli--1/2 gram. 50 cc. of water and 50 cc. of glycerine. All mixed together--prolonged shaking. B. E. is supposed to contain not only the extract of the body of the tubercle bacilli, as in T. R., but also its soluble products (which in the case of T. R. were discarded in setting aside the supernatant fluid). THEORIES OF TUBERCULIN REACTION