154 



Scientific Proceedings (113). 



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 collabor- 

 ators, 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. 

 The species or class reaction (heteroreaction) is present, but less 

 pronounced than in higher forms. In lower adult vertebrates the 

 individuality (homoio) reaction is definitely found; but there are 

 some indications that it is as yet not so pronounced as in higher 

 vertebrates. As far as we can judge from experiments carried 

 out for other purposes, we may therefore conclude that an onto- 

 genetic and phylogenetic evolution of the individuality reaction 

 has taken place and that the immunity reaction is probably 

 dependent upon a special application of this evolution of the 

 species and individuality differentials. 



4. We have previously stated that in guinea pigs the indivi- 

 duality reaction is found in animals of various age, sex, and in 

 pregnant animals. 



For some time past we have been carrying on more extensive 

 studies on the influence of these secondary factors in guinea pigs. 

 We varied the age of the host as well as of the donor in order to 

 study the effect of age on the four variables mentioned above. 

 Thus far we can state that the lymphocytic reaction may be very 

 marked not only if the tissue is transplanted into adults, but even 

 if it is transplanted into guinea pigs a few days old. 



The individuality reaction exists in pregnant as well as in non- 

 pregnant guinea pigs. Autotransplantation of the thyroid gland 

 in pregnant animals led in some cases to abortion. This did not 

 noticeably influence the individuality reaction. Pregnancy did not 

 improve the growth of the transplanted thyroid ; on the contrary in 



