CHEONIC INFECTIOUS DISEASES 97 



proved ineffective. In veterinary medicine tuberculin 

 has only been used as a diagnostic agent, and in it 

 we have a valuable preparation for such purpose at 

 our disposal. 



In addition to the above tuberculin, Koch subse- 

 quently introduced other remedial preparations of 

 tubercle bacilli. Instead of the toxin produced by 

 growth of the bacilli in a fluid medium, he made use 

 of extracts of the organisms themselves. He took 

 highly virulent cultures of tubercle bacilli, dried 

 them in vacuo, and triturated them in a mortar. 

 The resulting powder was treated with sterile dis- 

 tilled water and submitted to centrifugalisation. The 

 supernatant clear, but opalescent, fluid was then 

 removed from the debris, and 20 per cent, of glycerine 

 added as a preservative. To this Koch gave the 

 name of *' Tuberkulin-0." The solid residue, thus 

 freed from soluble toxins, was then dried, and the 

 process of extraction by triturating with 20 per cent, 

 glycerine solution, and then centrifugalising, was 

 repeated several times, the fluid each time being 

 preserved, and the whole finally mixed together. 

 This mixture constitutes the new tuberculin. 



Action of Tuberculin . — It is found that if a small 

 quantity, 30 to 60 minims, of the old tuberculin 

 is injected hypodermically into an animal suffering 

 from tuberculosis, very definite symptoms are pro- 

 duced. There is a rise of temperature of varying 

 intensity from 2*5° to 4° Fahrenheit, accompanied 

 by dullness and appearance of illness. The mode 



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