Abstract
Our methods of producing typhus vaccines with the murine strains of Rickettsiae has depended upon the inoculation of rats in which resistance had been reduced by a variety of procedures, the most consistently successful of which has been preliminary X-ray radiation. These methods have persistently failed to give adequate results with the European virus. This fact in itself constitutes further strong evidence that the two types of Rickettsiae are distinct and biologically fixed varieties. After much effort to apply the “rat” methods to the organism of the classical European disease we were finally persuaded that other methods of approach must be sought for obtaining accumulations of the European Rickettsiae adequate for practical purposes of immunization.
In a paper, now in press, the writers have reported the results of experiments in which the active immunization of guinea pigs against the European typhus virus was accomplished, both with the use of formalinized tissue culture vaccines and by methods of sero-vaccination. While this work was going on, Kligler and Aschner 1 published observations on a method of successful animal immunization with formalinized tissue culture vaccine, similar in all important principles to the method which we are using.
Since the development of a tissue culture technique for producing vaccines in amounts adequate for practical purposes appeared the most hopeful direction of effort, we have tried for a long time to improve the technique of making such cultures, particularly in regard to increasing the volumes of the tissue cultures themselves.
In studying the general problem of tissue cultures, one of the writers (Zinsser) in collaboration with Schoenbach, turned his attention to observations on what may be called the physiology of tissue cultures in general, particularly as regards changes in pH, oxygen consumption and oxydation-reduction potentials.†
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