CHAPTER IX. 



Contagious and Infectious Diseases 



TUBERCULOSIS 



THE DIAGNOSIS OF TUBERCULOSIS 



The symptoms of tuberculosis in cattle are not sufficiently 

 prominent, except in advanced stages or when superficially lo- 

 cated, to enable one to diagnose this disease by the ordinary meth- 

 ods of physical examination, and the cattle may, without showing 

 any clinical symptoms, be in such a stage of tuberculosis as to ren- 

 der them capable of spreading disease. Indeed, an animal may be 

 fat and sleek, eat and milk well, have a bright,' glossy coat and be 

 apparently in the pink of condition, and still be passing tubercle 

 baccili through the feces or by an occasional cough, and thus en- 

 danger all the healthy cattle in the herd. Consequently, advan- 

 tageous aids to diagnosis as animal inoculation, biological tests, 

 serum agglutination reaction, and the tuberculin test are made use 

 of in arriving at a definite opinion relative to the presence or ab- 

 sence of this disease. The value of all but the last of these is dis- 

 counted by the technique required and by their impracticability, 

 while the tuberculin test is most satisfactory and is the best diag- 

 nostic agent known for the disease. 



THE ORIGIN OF THE TUBERCULIN TEST 



Tuberculin was invented b}' Kck^Ii in 1890 and was first used 

 experimentally in treating tuberculosis in man. In these cases it 

 was observed that its injection was followed by a rise of tempera- 

 ture, which led veterinarians to apply tuberculin to suspected ani- 

 mals to see if a similar reaction resulted. Numerous experiments 

 showed this to be the case, and since 1891 the use of tuberculin as 

 a diagnostic agent for tuberculosis of cattle has been almost uni- 

 versally adopted in all parts of the civilized world. No one thinks 

 of accepting tuberculin as an absolutely infallible agent, but it is 

 immeasurably more dependable than any other method that has 

 ever been used. 



