TUBERCULOSIS OF THE COW 135 



broth for some months, filtering out the bacilli through porce-j 

 lain, and evaporating to one-tenth its bulk. It is therefore 

 essentially a concentrated glycerine solution of the extra- 

 cellular toxins of the tubercle bacillus. 



The nature of the test rests upon the fact that when 

 tuberculin is injected into a healthy animal no constitutional 

 disturbance takes place, but if the animal is affected with 

 tuberculosis a considerable rise of temperature and other con- 

 stitutional effects are manifest. 



To carry out the test properly requires skill and attention. 

 The temperature of the cow is taken on several occasions 

 beforehand to ascertain the normal temperature of the animal. 

 A variation of 1^ degrees F. may be met with in animals in 

 perfect health. The tuberculin is injected subcutaneously 

 during the evening of the day on which the preliminary tempera- 

 tures have been taken, and so as to allow an interval of about 

 10 hours before next morning's milking. The temperature 

 is taken every 2 hours from the 10th to the 18th to 20th 

 hour after the injection. The more numerous the temperature 

 takings the less liability of error. Some practical veterinary 

 surgeons take only 3 or 4 temperature records after injection. 

 The cows should be under as quiet and natural conditions as 

 possible during the test. A rise of 2*0 degrees F. above the 

 normal, if gradual and distributed over a time period of several 

 hours with gradual decline, indicates a positive reaction. A 

 sharp brief rise and fall of the temperature does not con- 

 stitute a positive reaction. Some authorities regard a rise 

 of 1'5 degrees as constituting a positive reaction, others 

 consider a rise of no more than this as merely suspicious. 



The Chicago tuberculin test ordinance requires : " The 

 temperature shall be taken at least 4 times on the day pre- 

 ceding the inoculation, and at least 6 times on the day follow- 

 ing the inoculation, at not less than 2 hour intervals. A rise 

 of 2 degrees over the average temperature on the day preced- 

 ing the inoculation shall be considered a positive test. If a rise 

 of from 1^ degrees to 2 degrees is obtained, the results shall be 

 considered doubtful, and the animal subjected to a later retest." 



I am enabled by the kindness of Sir John McFadyean to 

 give the following examples of reactions to tuberculin, all 

 from the one herd : 



