260 SUSCEPTIBILITY AND IMMUNITY. 
oculation into susceptible animals, neutralizes the pathogenic power 
of these cultures. 
They have shown by experiment that the blood of a rabbit which 
has an acquired immunity against tetanus, mixed with the virulent 
filtrate from a culture of the tetanus bacillus, neutralizes its toxic 
power. One cubic centimetre of this filtrate was mixed with five 
cubic centimetres of serum from the blood of an immune rabbit and 
allowed to stand for twenty-four hours ; 0.2 cubic centimetre of this 
injected into a mouse was without effect, while 0.0001 cubic centi- 
metre of the filtrate without such admixture was infallibly fatal to 
mice. The mice inoculated with this mixture remained immune for 
forty to fifty days, after which they gradually lost their immunity. 
The blood or serum from an immune rabbit, when preserved in a 
dark, cool place, retained its power of neutralizing the tetanus tox- 
albumin for about a week, after which time it gradually lost this 
power. The blood of chickens, which have a natural immunity 
against tetanus, was found not to havea similar power. Behring 
and Kitasato have also shown that the serum of a diphtheria-immune 
rabbit destroys the potent toxalbumin in diphtheria cultures. It 
does not, however, possess any germicidal power against the diph- 
theria bacillus. 
Ogata, in 1891, reported that he had succeeded in isolating from the 
blood of dogs and of chickensa substance to which he ascribes the nat- 
ural immunity of these animals from certain infectious diseases, and 
the power of their blood to protect susceptible animals from the same 
diseases. This substance is soluble in water and in glycerin, but in- 
soluble in alcohol or ether, by which it is precipitated without being 
destroyed. Its activity is neutralized by acids, but not by weak 
alkaline solutions. Ogata supposes the substance isolated by him to 
be the active agent in blood serum by which certain pathogenic bac- 
teria are destroyed, as shown by the experiments of Nuttall, Buchner, 
and others. Hankin had previously isolated an albuminoid sub- 
stance from the spleen and blood of the rat, to which he ascribed the 
immunity of this animal from anthrax. This substance, according 
to the author named, is a globulin; it is insoluble in alcohol and in 
distilled water, and does not dialyze. 
Tizzoni and Cattani ascribe the protection of animals which have 
acquired an immunity against tetanus to the présence of an albumi- 
nous substance which they call the tetanus-antitoxin. This they 
have isolated from the blood of immune animals. They arrive at 
the conclusion that it is a globulin, or a substance which is carried 
down with the globulin precipitate, and that it is different from the 
globulin, above referred to, obtained by Hankin from animals im- 
mune against anthrax. 
