Abstract
1. We may distinguish between two sets of factors determining the fate of transplants: (a) primary or constitutional; (b) secondary or extraneous factors. The former comprise the individuality and species differentials, and possibly organ specific factors; the latter include such factors as age, sex, pregnancy, infection and immunity. There are in addition general factors as oxygen supply, character of circulation and temperature; the latter we shall at present leave out of consideration.
If we take the subcutaneous transplantation of the thyroid gland as type, we find the following variables which may be influenced by the two sets of conditions: (a) the amount of surviving parenchyma and its growth energy; (b) the behavior of the connective tissue cells; (c) of blood and lymph vessels, and (d) of the lymphocytes of the host towards the transplant.
2. In a series of earlier papers we have analysed the effect of the individuality and species differentials on these four variables and we found a gradation in the effects observed which was in accordance with the relationship between host and graft.
3. Tyzzer and others, and especially Murphy and his collaborators, have shown that the appearance of lymphocytes in the case of transplanted tumors is an index of immunity against these tumors. Murphy and Rous showed that such an immunity cannot be produced in chick embryos, even in the case of hetero tumors, and Bullock and Rohdenburg found the same in newly born rats.
An analysis which we undertook recently of the results of transplantation carried out by numerous investigators in various classes of animals very strongly suggests the conclusion that the individuality (homoio) reaction is usually absent in embryonic and adult invertebrates and in embryonic forms of vertebrates.
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