GENUS BACTERIUM 253 



high speed. The supernatant fluid, known as TO (Tuberculin- 

 Oberschicht), contains the water-soluble constituents of the 

 bacterium, gives no precipitate on the addition of 50% 

 glycerin, and has the same physiological action as the old 

 tuberculin. The residue, TR ( Tuberculin- Ruckstand) after 

 pouring off TO, is again dried, ground up, and again shaken 

 in water and centrifugalized: This process is repeated several 

 times, and eventually, after three or four repetitions, all the 

 TR goes into emulsion. The total volume of water used for 

 these TR extractions should not exceed 100 cc. All of the TR 

 emulsions are then mixed together. This TR gives a precipi- 

 tate with 50% of glycerin, and was supposed by Koch to con- 

 tain substances important in producing an antibacterial im- 

 munity. 



A number of other preparations of tuberculin have been 

 made. Koch 10 combined the TO and TR to form a tuberculin- 

 bacillary emulsion. It consists of 5 milligrams of pulver- 

 ized tubercle bacteria in each cubic centimeter. Buchner and 

 Halm prepared a tuberculoplasm by crushing the bacteria 

 under a presure of 400 atmospheres. It possessed the proper- 

 ties of Koch 's TR. There are several other preparations made 

 but they are of no special value in veterinary work. The 

 practical use of the tuberculins are (1) the old tuberculin to 

 give a reaction for the purpose of the diagnosis of tuberculosis 

 and (2) the new tuberculin for therapeutic value and to im- 

 munize animals against tuberculosis. The old tuberculin is 

 also used to some extent in the treatment of tuberculosis. 20 In 

 veterinary practice the old tuberculin is used for diagnosis. A 

 purified tuberculin is prepared by precipitating the old tuber- 

 culin w r ith 95% alcohol and washing the sediment with 70% 

 alcohol until the filtrate is clear and dry. A solution of from 

 0.05 to 0.1% of the dried precipitate is made in a sterile nor- 

 mal salt solution. This is employed for the Wolff-Eisner or 

 ophthalmic test. 



19 Koch. Deut. med. Woch., 1901, 



20 A number of physic ians have reported good results in the 

 therapeutic use of old tuberculin in selected cases. Its use for this 

 purpose has not been successful in cattle. 



