144 ESSAYS ON BACTERIOLOGY. 



which Koch himself has recently admitted and ex- 

 plained. But the diagnostic significance of the tu- 

 hercnlin injection remains. Until recently thia 

 method has, except in the hands of a few experiment- 

 ers, been restricted to the diagnosis of the disease in 

 animals. Here its value and reliability are now gen- 

 erally recognized by veterinarians. It is hardly too 

 much to say that to-day the efforts for the eradication 

 of tuberculosis among cattle and for the protection of 

 the public against tuberculous meat and milk center 

 about the tuberculin diagnos-is. Of late the profes- 

 sion has been recovering from the fear of harm by this 

 procedu.re, and on good grounds. The dangers have 

 certainly been much exaggerated. The hypodermic 

 injection of from one-half to three milligrams of tu- 

 berculin will usually produce, in a person having any 

 form of tuberculosis, a recognizable reaction sufficient 

 to establish the diagnosis. The pulse quickens, the 

 temperature rises, and there is more or less accom- 

 panying local and general disturbance, all of which 

 subside within a few hours or days. In order that 

 the results may be correctly interpreted and possible 

 dangers avoided, certain precautions and preparations 

 are necessary. The tuberculin must be genuine and 

 not too old. It must have been proven free from con- 

 tamination, and should, if possible, have been pre- 

 viously' tested upon a known case of tuberculosis. 

 The patient's pulse and temperature should have been 

 recorded at regular intervals for several days, and a 



