The Occurrence of Specific Immunity Principles in the Blood of Vaccinated Calves

(From the Rockefeller Institute !or Medical Research, New York.) The immunity which human beings develop towards vaccinia, after a successful vaccination, is the classical example of an artificially induced active immunity. The duration of the immunity to vaccinia is variable but extends frequently over many years. Many animals are subject to inoculation with vaccinia and they show, as in the case of man, a state of immunity following the disappearance of the successful vaccination. The calf, as is well known, is now generally employed for the production of the vaccine-virus which is used to protect human beings from smallpox. At one period in the development of specific serum therapy an attempt was made to utilize the immune principle which it was presumed existed in the blood of animals which have passed through a successful vaccination. The hope was entertained that, possibly, the serum of the vaccinated calf might exercise curative properties upon persons suffering with smallpox. This hope has not been realized. In order to prove the existence of immunity principles in the blood of vaccinated animals the at tempt was made to protect, by inoculation of the blood of these calves and monkeys, fresh animals from vaccinia. In spite of some successful results the experiment may be said to have often failed.' -The failure of the blood of vaccinated animals regularly to confer passive immunity or to exert curative effects cannot be held to disprove the existence in the blood of immunity substances. Tests of the kind mentioned are exceedingly gross. Moreover,