HORMONES AND INDIVIDUALITY DIFFERENTIALS 145 



stimulation of the thyroid gland in the guinea pig ; they should therefore pro- 

 mote the growth of thyroid transplants and help the latter to overcome the 

 injurious effects which a disharmony between the individuality differentials 

 of host and transplant exert on the survival and growth of the latter. How- 

 ever, Martin Silberberg, who carried out such experiments, noticed that the 

 hypertrophy of the transplanted organ is less readily accomplished than that 

 of the non-transplanted thyroid gland, a finding with which our own is in 

 agreement and which can be understood if we consider the less favorable 

 circulatory conditions in a transplanted organ and a certain inadequacy in 

 the relations between stroma and transplanted parenchyma whenever a dis- 

 harmony exists between the individuality differentials of host and transplant. 

 Silberberg furthermore made the interesting observation that a thyroid 

 gland, rendered hypertrophic previous to transplantation by injections of 

 anterior pituitary extracts, can be less readily successfully transplanted than 

 a non-hypertrophic gland. Apparently the state of hypertrophy corresponds 

 to an increased differentiation of the tissue, which makes the organ less 

 resistant to the injury inflicted during the process of grafting. But on the 

 whole, this investigator found favorable effects of injections of anterior 

 pituitary extract on the homoiogenous thyroid if the injections were begun 

 after the thyroid had been transferred to the new host. However, the results of 

 the experiments of Silberberg, as well as our own in similar experiments, 

 showed a certain variability, and on the whole, in the large majority of trans- 

 plantations the action of the thyroid-stimulating hormone was not able to 

 overcome the unfavorable results of homoiogenous transplantation of the 

 thyroid gland in the guinea pig. These results agree with those of Bayer and 

 Wense, who showed that injections of pregnancy urine, containing prolan, 

 did not exert a beneficial effect on intra-ocular, homoiogenous transplants of 

 testicle in the rabbit. 



There is another condition in which hormones might possibly affect the 

 fate of the transplant, namely pregnancy. In pregnant guinea pigs the reac- 

 tions against homoiogenous transplants of thyroid, cartilage and fat tissue 

 were severe in the majority of cases, even during early pregnancy of the host, 

 but in some animals the reaction was relatively mild. It was conceivable that 

 pregnancy exerts its effects by causing undernourishment of the transplants. 

 However, in control experiments, in which young guinea pigs with an initial 

 weight of 195-225 grams were underfed for a period of 18 days, so that the 

 end weight was between 160-185 grams, the grades of the homoiogenous 

 thyroid transplants were similar to those in well-fed animals, or they were 

 even somewhat better in the underfed guinea pigs. 



As already mentioned on the basis of experiments with transplantations of 

 the thyroid gland, Christiani (1900-1905) stated that an endocrine deficiency 

 is needed for the successful transplantation of an endocrine organ. He attrib- 

 uted this favorable result of a diminution in the amount of the endocrine 

 organ, in particular the thyroid present in the host to the improvement in the 

 vascularization of the graft in animals deficient in the production of the 

 thyroid hormone. However, he actually observed merely an increased size and 



