368 AGRICULTURAL BACTERIOLOGY. 



it is a matter of wisdom for such measures to be adopted 

 as will prevent the dissemination of the disease from these 

 animals to the rest of his herd. As a prerequisite for prevent- 

 ing such dissemination the first absolute necessity is to 

 determine all cases of tuberculosis that may be among the 

 animals. Whatever he may propose to do with such animals, 

 it is certainly a matter of first importance that the owner 

 recognize them. 



The Tuberculin Test. The only method of detecting all of 

 these cases is by the tuberculin test. This test is certainly of 

 use to agriculture, although, because of misunderstanding, 

 there has been a prejudice raised against it. Tuberculin was 

 first prepared and used by Professor Koch. The essential 

 facts concerning its use are as follows : 



Tuberculin is a product of the growth of tubercle bacilli, 

 but it is prepared in such a way that it contains no bacilli and 

 cannot possibly produce tuberculosis. It is made by causing 

 the tubercle bacilli to grow in a broth containing glycerine. 

 After growing in such broth for some weeks, the bacilli pro- 

 duce certain toxic products which are soluble and, of course, 

 dissolve in the broth. The material is then treated (by filter- 

 ing) in such a way as to remove the bacilli, and the clear, 

 toxic-holding solution is tuberculin. Inasmuch as it does not 

 contain the bacilli, it cannot possibly excite the disease, and its 

 use among animals cannot incite tuberculosis as has been 

 sometimes ignorantly claimed. 



Although containing no bacilli, tuberculin does contain the 

 toxins which the bacilli produce, and these toxins, if inoculated 

 into an animal in sufficient quantity, would have a poisoning 

 effect. When injected in small quantity the material has no 

 effect upon the healthy individual ; but if the individual is 

 already affected with the disease this inoculation produces a 

 noticeable reaction. It results in a marked rise in temperature, 

 which soon disappears, the animal resuming its normal condi- 



