354 BACTERIOLOGY. 



SUSCEPTIBILITY OF ANIMALS TO TUBERCULOSIS. 

 The animals that are known to be susceptible to tuber- 

 culosis are man, apes, cattle, horses, sheep, guinea-pigs, 

 pigeons, rabbits, cats, and field-mice. White mice, dogs, 

 and rats possess immunity from the disease. 



TUBERCULIN. The filtered products of growth from 

 old fluid cultures of the tubercle bacillus represent what 

 is known as tuberculin a solution containing a group of 

 proteid substances possessing most interesting properties. 

 When injected subcutaneously into healthy subjects tuber- 

 culin has no effect ; but when introduced into the body 

 of a tuberculous person or animal a pronounced systemic 

 reaction results, consisting of sudden but temporary ele- 

 vation of temperature, with, at the same time, the occur- 

 rence of marked hypersemia about the tuberculous focus 

 a change histologically analogous to that seen in the 

 primary stages of acute inflammation. This zone of 

 hypersemia, with the coincident exudation and infiltra- 

 tion of cellular elements, probably aids in the isolation 

 or casting off of the tuberculous nodule, the inflamma- 

 tory zone forming, so to speak, a line of demarcation 

 between the diseased and healthy tissue. 



As a curative agent for the treatment of tuberculosis, 

 tuberculin has not merited the confidence that was at 

 first accorded to it. Its field of usefulness is now 

 almost limited to the diagnosis of obscure cases, and 

 even for this purpose it is less frequently employed 

 than formerly. 



In veterinary medicine it has proved much more 

 trustworthy as a diagnostic aid, and is practically 

 everywhere in use for the detection of incipient tuber- 

 culosis in cattle. 



