636 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1907. 
certain bacteria, that a degree of immunity or protection which it is 
impossible to obtain even after very prolonged treatment with the 
fluid portions of cultures, can be secured quickly when small quan- 
tities of the living or even dead micro-organism are injected into the 
body. A high degree of bacterial immunity has been secured up to 
now for a small number of micro-organisms by vaccination—by the 
method introduced by Pasteur—for several animal diseases, notably 
anthrax or splenic fever, fowl cholera, and black-leg. In these cases 
ihe living attenuated micro-organisms are employed. 
Neither lasting nor marked immunity in tuberculosis can be ob- 
tained by the inoculation of cultures of tubercle bacilli killed by heat, 
sunlight, or other agency. Dead tubercle bacilli are poisonous and 
bring out a striking reaction of the organism, but this reaction does 
not confer immunity to subsequent inoculations of the living germ. 
It may well be that the dead bacilli, especially if reduced to im- 
palpable powder so as to facilitate absorption, may after injection 
raise the powers of resistance in the organic forces, although the 
height of the sustained forces is not sufficient to enable the body to 
throw off completely the living infecting organism. It is easy to 
prove that the animal organism is modified by the development within 
it of the tubercle bacilli; and merely disposing of dead bacilli in- 
creases its power of reaction against a second injection of dead 
tubercle bacilli; the second action being much more vigorous than the 
first. The experiments of Koch which immediately preceded the dis- 
covery of tuberculin clearly demonstrated that tuberculous guinea 
pigs into which tubercle bacilli are reintroduced subcutaneously react 
in a very especial manner. An active inflammatory process develops 
about the site of second inoculation which eventually brings about the 
expulsion of bacilli with the exudations; a voluminous slough forms, 
which, when shed, carries with it a large number of bacilli; and this 
shedding is followed neither by the formation of a permanent ulcer 
nor hypertrophy of the neighboring glands, a regular result of the 
primary inoculation. The tubercular organism reacts in the same 
manner to dead as to living bacilli; the tuberculous animal has ac- 
quired immunity against reinfection or reintoxication by the tubercu- 
lous virus, which, however, in no way prevents the first inoculation 
from becoming generalized and setting up a tuberculosis of almost all 
the organs. 
If we attempt an interpretation of these phenomena we can con- 
clude that the organism, once it is poisoned with tubercle virus, 
becomes supersensitive to the tubercle poison. This supersensitive- 
ness is displayed in the manner of reaction upon reinoculation of the 
tuberculous organism to tuberculin and to dead and living tubercle 
bacilh. But the organism poisoned with dead tubercle bacilli is not 
im reality tuberculous; it is, however, sensitized. In keeping with 
