148 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



individuality differentials. But in all these experiments, the degree of strange- 

 ness of the individuality differential of the host was a factor in determining 

 the effectiveness of the hormonal stimulation on the survival and growth of 

 the transplant; if the disharmony between the individuality differentials of 

 host and transplant was diminished, the results were better. The increase in 

 growth momentum acts in these instances in principle in the same way as this 

 factor acts in tumors, which thereby also are enabled, to a certain extent, to 

 overcome the injurious action of non-adequate individuality differentials by 

 an increased growth momentum. In some organ transplants, factors inherent 

 in the transplanted cells seem to predominate over the endocrine factors, and 

 such transplants are largely unaffected by an increase in hormone stimulation ; 

 or a minimal amount of such stimulation may be sufficient and its effectiveness 

 cannot be increased by additional amounts of hormones. As stated already, in 

 addition to these factors, the age of the host, and especially of the transplant 

 may affect the results. 



In earlier investigations concerning these problems emphasis was laid on the 

 importance of the creation of a deficiency in the amount of the corresponding 

 endocrine organ of the host, as far as the success of the fate of the graft was 

 concerned. But in reality, there is hidden behind this diminution in the amount 

 of the host endocrine organ an increase in the stimulation of the transplant by 

 an increased function or an increased production of the effective hormone in 

 the host. We may illustrate this interpretation by a reference to the condi- 

 tions noted by us in the development of compensatory hypertrophy of the 

 thyroid gland in the guinea pig. We found that this depends upon the balanc- 

 ing of two hormone effects. In the first place, the administration of thyroid 

 hormone tends to diminish the growth and hormone production of the normal 

 thyroid gland of the treated animal. The thyroid hormone given off by the 

 intact thyroid gland, correspondingly tends to limit these activities. On the 

 other hand, the thyroid-stimulating hormone of the anterior pituitary gland 

 opposes this effect by stimulating the thyroid gland and by causing hyper- 

 trophy. The normal condition of the thyroid gland is the consequence of a 

 certain equilibrium between these two opposing tendencies, and this equilibri- 

 um can be changed by suppressing or enhancing one of the two factors in- 

 volved. By excising a considerable portion of the thyroid gland, the amount 

 of thyroid hormone given off is diminished and, correspondingly, the stimu- 

 lating activity of the anterior pituitary gains the upper hand; on the other 

 hand, an increased activity of the thyroid causing a depression in the func- 

 tion of the anterior pituitary has the opposite effect. Somewhat similar con- 

 siderations apply to the equilibrium in the thyroid gland, ovary, and perhaps 

 also the islands of the pancreas and some other organs with internal secretions. 

 It is not certain in these cases whether the intrinsic hormone, as for instance, 

 the thyroid hormone, acts directly on the organ in which it originates or 

 whether it acts on the controlling endocrine gland, the anterior pituitary. In 

 the case of the ovary, estrogen exerts its effects evidently by way of the 

 anterior pituitary. We may therefore conclude that the results of extirpation 

 of an endocrine organ depend on the consequent surplus function of another 



