T H E Individuality Differential and T H E Reactions against Transplanted Tissues and Tumors with Particular Cytic Reaction Reference to the Lympho-

The similarity or difference in the character of the individuality-, raceand species-diff erentials between host and transplant determines the reaction of the host against the transplant in the case of normal tissues as well as of tumors and in addition it determines the active immunity against tumor growth. In my earlier publications, I have compared this series of differentials and reactions with a spectrum which may be designated as the spectrum of differentials. This series of differentials can be compared with the colors of the optical spectrum with the reservation that the areas of several of these spectra overlap, the averages in each case corresponding to certain colors. The spectrum of wave-lengths can be compared with the continuity of genes composing these differentials. However, the genetic composition of these differentials is as yet very imperfectly known and we depend therefore on the general terms of the differentials; they serve a practical purpose, expressing relationships between hosts and transplants. We have established that each differential is genetically composed of multiple factors. As to their number, no definite statement can be made. It is possible that the totality of the chromosomes with exception of the sex chromosome participates in the composition of the differentials. It will be necessary to use the finest reactions available for the separation of the various differentials after transplantation. Number of takes and the growth of the ordinary transplantable tumors represent