BACILLUS OF TUBERCULOSIS. 291 



The new tuberculin formed by either of these methods 

 is a watery extract of the soluble portions of the un- 

 altered tubercle bacilli. As can be readily seen, in a 

 preparation thus made contamination is difficult to 

 avoid, freedom from intact bacilli is uncertain, and the 

 strength of the solution prepared at different times is 

 variable. Twenty per cent, of glycerin is added to 

 preserve the tuberculin from contamination. After 

 three years of trial the results obtained with the new 

 tuberculin preparations cannot be considered to have 

 exerted either very different or very superior effects to 

 the older product. 



As to the results obtained in general the reports are 

 as yet conflicting. Lupus seems to be decidedly bene- 

 fited for a time both by the old and the new tuberculin. 

 Relapses are, however, common. On advanced phthisis, 

 laryngeal tuberculosis, arid other tubercular processes 

 no effects have been noted, and nearly every one dis- 

 approves of their use in these cases as well as in those 

 where mixed infection is suspected ; even in cases of 

 beginning infection, opinions, as a whole, are not very 

 enthusiastic. The new tuberculin is, except when 

 prepared with the utmost care, .a dangerous substance, 

 for Trudeau, Baldwin and others found that guinea-pigs 

 injected with it not only did not become immunized, 

 but actually became infected from the living bacilli in 

 the fluid. 



The chief use to which tuberculin has been put is as 

 an aid to the diagnosis of tuberculosis in cattle and 

 human beings, and for this purpose it has proved to be 

 of inestimable value. Numerous experiments made by 

 veterinary surgeons show that the injection of tuber- 

 culin in tuberculous cows in doses of 25 to 50 centi- 



