126 Bulletin 65. 



The explanation of the reaction under tuberculin may be very 

 simply stated. The dose is made so small that it will not affect a 

 healthy cow under ordinary conditions. In the slightly diseased 

 cow the system contains a certain amount of tuberculin produced 

 by the bacillus in the tubercles, but to this the system has become 

 accustomed and it causes no very appreciable fever. But when 

 in addition to this we introduce into the body of this cow the 

 small amount of tuberculin, used for the test, the increased dose 

 acts on tubercle and nervous centres alike and a fever is produced. 

 So evenly balanced has been the tolerance acquired, and the 

 amount of poison tolerated with impvmity, that four drops of 

 tuberculin will as a rule produce this elevation of temperature in 

 the moderately tuberculous cow. 



Objection to Ttiberculin as a Test. — ist. The temperature some- 

 times rises in a non-tuberculous cow after the use of the tuberculin. 



This is true. So does the temperature sometimes rise in a non- 

 tuberculous cow when no tuberculin has been employed. Every 

 animal is liable to suffer from inflammation and fever, and if such 

 inflammation and fever set in after the use of the tuberculin test 

 they are liable to be charged to it as their cause. This is a valid 

 argument against the reckless popular use of the tuberculin, but 

 surely not against its use in skilled hands. The person who uses 

 the tuberculin on cattle must be a trained veterinarian, acquainted 

 with the different diseases of cattle and on his guard against con- 

 founding any one of these with the temporary fever caused by 

 tuberculin in the consumptive. If it is claimed that every rise of 

 the body temperature after the use of tuberculin must necessarily 

 demonstrate the existence of tuberculosis, then truly tuberculin 

 will be discredited. But if it is held rather that a rise of tempera- 

 ture after tuberculin, in a cow that furnishes to the most careful 

 and skillful comparative pathologist no evidence of other disease, 

 implies the existence of tuberculosis, the claim is substantially 

 correct. To secure the valuable testimony of tuberculin, the 

 practitioner must be highly skilled in the diseases of the animal 

 operated on. If he is not he will be occasionally misled. 



Again heat or bulli?ig may come upon a cow after the use of the 

 tuberculin and the temperature will rise two or three degrees. 

 To call such a cow tuberculous would be inexcusable careless- 



