Abstract
Eight years ago one of us has shown that through the influence of chemical and physical factors it is possible to decrease the energy of growth of tumor-cells without killing the cells. 1 While a certain degree of injury kills the cells, a graded decrease in the action of the external agency leads to corresponding gradations in the decrease in the energy of growth of the cells. Thus it is possible to obtain tumor material which is still alive, but which gives rise to a very insignificant growth in many instances, and the initial growth of which is in many cases followed by a spontaneous retrogression. At that time we considered the possibility that such tumor material of experimentally decreased virulence might serve as a vaccine which might provide a certain protection against a second injection with more virulent material.
We tested therefore the influence of a first injection of such material upon the growth of a subsequent inoculation with tumor material. In the majority of cases both inoculations were separated by an interval of 10–20 days.
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