354 PROTECTIVE INOCULATIONS. 
have determined many of the chemical characters of the tetanus toxin. 
When in solution it is destroyed by a comparatively low temperature 
(55° C. for one hour) and by exposure to direct sunlight, but the dry 
powder resists a temperature of 120° C. It has not the properties of 
an alkaloid, as it is not dissolved by any of the usual solvents of these 
bodies—the only solvent thus far discovered is said to be water. It 
resembles the albumins and peptones in its failure to pass through 
a dialyzing membrane. The authors last referred to conclude their 
summary of results as follows: 
‘‘The appended table shows that the tetanus poison, like that of diph- 
theria, in its behavior as regards the action of light, heat, chemical agents, 
and dialysis, as also its solvents, the agents which precipitate it, and its action 
upon living animals, closely resembles the poisons of serpents (Naja tripu- 
dians, Crotalus, etc.). As to the chemical nature of this group of substances, 
we can at present only say that they rather have the characters of collodial 
substances than otherwise, and more nearly resemble the albuminoid bodies 
than the bases. We do not, however, reject the very probable hypothesis 
that these toxins are acids or bases, or other very unstable, peculiar substances, 
which are closely united with colloidal substances, as is the case, for example, 
with the alkali and acid albumins and so many other albuminous bodies.” 
While the exact nature of the toxic substance contained in tetanus 
cultures has not been determined, we probably cannot, at present, do 
better than to continue to speak of it as a “toxalbumin.” 
Kitasato (1891) was not able to produce immunity in mice by in- 
oculations with minute doses of the poison, or with a filtrate which 
had been exposed to various degrees of temperature by which its 
activity was diminished or destroyed. But immunity lasting for 
about two months was produced in rabbits by inoculating them with 
the filtrate from a culture of the tetanus bacillus, and subsequently, 
in the same locality, with three cubic centimetres of a one-per-cent 
solution of terchloride of iodine; this last solution was injected sub- 
cutaneously in the same dose at intervals of twenty-four hours for five 
days. Of fifteen rabbits treated in this way six proved to be immune 
against large doses of a virulent culture of the tetanus bacillus. The 
same treatment was not successful in producing immunity in mice or 
guinea-pigs, but the important discovery was made that a small quan- 
tity of blood (0.2 cubic centimetre) from an immune rabbit, when in- 
jected into the abdominal cavity of a mouse, gave it immunity from 
the effects of inoculations with the tetanus bacillus. Moreover, mice 
which were first inoculated with a virulent culture of the bacillus, and, 
after tetanic symptoms had appeared, received in the cavity of the 
abdomen an injection of blood serum from an immune mouse, were 
preserved from death. The power of the blood of an immune animal 
to neutralize the tetanus poison was further shown by mixing the fil- 
