396 BACTERIOLOGY. 
to the septicemic class of organisms which spreads 
through the body, and by their growth and increase 
produce their effects, but, on the contrary, remains 
localized at the original point of infection. It pro-— 
duces, however, in its growth a most powerful toxin. 
The treatment of tetanus is, therefore, directed against 
the production of toxin and its neutralization in the 
body. The methods originally proposed by Behring and 
by Roux for producing a curative serum consisted 
chiefly in weakening the tetanus toxin by means of 
chemical disinfectants (iodine trichloride, Gram’s and 
Lugol’s solutions), so that when inoculated into the 
test-animals they produced comparatively little reac- - 
tion. At the present time we inject the pure unaltered 
toxin either alone in small doses or along with anti- 
toxin. After the first dose of toxin the animals acquire 
a certain tolerance which enables them to stand a dose 
of a less attenuated toxin or of a greater amount of un- 
changed toxin. Thus by gradually increasing the doses 
or the strength of the toxin administered, the animals 
are finally able to bear injections of large quantities of 
the strongest toxin. 
These immunizing experiments in tetanus have borne 
practical fruit, for it was through them that the prin- 
ciple of serum-therapeutics first bccame known—the 
protective and curative effects of the blood-serum of 
immunized animals. It was thus shown that animals 
could be protected from tetanus infection by the pre- 
vious or simultaneous injection of tetanus antitoxin, 
provided that such antitoxic serum was obtained from 
a thoroughly immunized animal; and from this it was 
assumed that the same result could be produced in natu- 
ral tetanus in man; but, unfortunately, the conditions 
