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, and 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- 
