PROTECTIVE INOCULATIONS. 333 
quantity (thirty-five cubic centimetres) of cord which had been kept 
for five or six days. In discussing his results Roux calls attention to 
the fact, which had been developed during his experiments, that the 
virulence of the spinal cord of rabid animals does not depend entirely 
upon the length of time it has been kept, but that large doses of cord 
kept as long as twelve days will sometimes produce hydrophobia when 
injected into the circulation of dogs, when smaller doses of cord kept 
five or six days prove to be inoffensive. He supposes that during 
desiccation the virus may not be equally acted upon throughout the 
cord, but that certain “islands” in the central portion may remain 
living and virulent when all the rest has been modified. A practical 
point with reference to the preservation of virulent material is referred 
to by Roux in a note published in the Annels of the Pasteur Insti- 
tute. This is the fact that when preserved in glycerin, portions of 
the central nervous system retain their virulence for considerable 
time. Other forms of virus, e.g., vaccine, may also be preserved in 
the same way. 
Centanni (1892) has succeeded in making rabbits immune by in- 
oculating them with an attenuated virus obtained by subjecting viru- 
lent material to the action of an artificial gastric juice. After digestion 
for less than twelve hours the virus still kills rabbits, when inoculated 
beneath the dura mater, but the period of incubation is considerably 
prolonged. After from twelve to twenty hours’ digestion it no longer 
kills rabbits, but causes an infection, from which they recover, and 
after which they are immune. 
Serum-therapy.—Tizzoni and Centanni (1892) have reported suc- 
cess in the treatment of infected rabbits by the use of blood serum 
from immune animals of the same species—immunized by the “Ital- 
jan method” above described. The animals experimented upon were 
inoculated with a “street virus” which produced paralytic rabies in 
rabbits and caused their death in from fourteen to eighteen days. 
The blood serum was obtained from rabbits which had been proved 
to be immune by resisting inoculations of virus of full strength on 
the surface of the brain. The blood serum, in doses of three to five 
cubic centimetres, was injected subcutaneously, or into the peritoneal 
cavity, or into the circulation. Injections were made into each animal 
(in all from eleven to twenty-six cubic centimetres) after the first symp- 
toms of paralytic rabies had appeared (on the seventh, the tenth, the 
eleventh, and the fourteenth day after infection). Four rabbits treated 
in this way fully recovered. In a subsequent experiment the bacteri- 
ologists named treated three rabbits with a dry antitoxin obtained by 
precipitation from the blood serum of immune rabbits. The precipi- 
