148 APPLIED BACTERIOLOGY 



rarely tuberculous, and become so by being infected through 

 .being kept with diseased cows. He therefore tests the 

 whole herd by means of tuberculin, and isolates those that 

 react as infected or suspicious. The herd is divided into 

 two sections, which are separated from one another and 

 have separate attendants and separate buildings ; they are, 

 however, allowed to mix when out in the fields. Every six 

 months the healthy side were tested with tuberculin, and 

 aiiy that were found to react were placed on the infected 

 side, while all calves were placed on the healthy side. The 

 animals in the tuberculous side which were obviously 

 tuberculous were got rid of, but those that were apparently 

 healthy were used for breeding. After this system had 

 been carried on for three years, the number of the tubercu- 

 lous animals in the herd had been reduced to a very con- 

 siderable extent, and the results seem to show the disease 

 may be to a large extent eliminated by the simple plan of 

 separating the animals that react to tuberculin from those 

 that do not, and removing all calves, as soon as they are 

 born, from their infected surroundings. 



Koch's Tuberculin Treatment. — Koch found that if a local 

 tubercular infection was set up in a guinea-pig by sub- 

 cutaneous injection, and later a Second subcutaneous 

 injection of the virulent or dead bacilli was made in 

 another part of the body, ulceration set up in the primary 

 tubercular nodule, the wound healing, and the animal did 

 not die of tuberculosis. From the result of prolonged 

 investigation Koch found that there appeared to exist in 

 tubercle bacilli an albumose-like body which exerted a 

 healing action in tuberculosis. He prepared a glycerine 

 extract of this body and called it 'tuberculin.' It was 

 prepared as follows : A peptone broth containing 5 per 

 cent, of glycerine was inoculated with virulent bacilli, and 

 incubated at blood-heat for about eight weeks. The culture 



