THE BACTERIUM TUBERCULOSIS 421 



Tuberculin. — ^The filtered sterile products of growth from 

 old fluid cultures of the tubercle bacillus represent what is 

 known as tuberculin — a solution containing a group of 

 protein 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 hyperemia about the tuberculous focus, 

 a change histologically analogous to that seen in the pri- 

 mary stages of acute inflammation. This zone of hyperemia, 

 with the coincident exudation and infiltration of cellular 

 elements, probably aids in the isolation or casting off of 

 the tuberculous nodule, the inflammatory zone forming, 

 so to speak, a line of demarcation between the diseased and 

 healthy tissue. 



As a curative agent for tuberculosis, tuberculin has not 

 proved worthy of the confidence that was at first accorded 

 to it. Its field of usefulness is now almost limited to the 

 diagnosis of obscure cases. 



In veterinary medicine it has proved trustworthy as a 

 diagnostic aid, and is practically everywhere in use for the 

 detection of incipient tuberculosis in cattle. 



Vaccination Against Tuberculosis. — Experiments by 

 Pearson and Gilliland, v. Behring, and others have shown 

 that it is possible to partly immunize animals with lowly 

 virulent tubercle bacteria of human origin. After one or 

 two injections with such organisms the animals showed for 

 a time some degree of tolerance to the more highly virulent 

 bovine strains. The results of experiments in this direction 

 have been so encouraging a? to justify further research 



