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 Annals 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- 

 ian 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- 



