156 LEO LOEB. 



CONSTANCY OF THE INDIVIDUALITY DIFFERENTIAL. 



This individuality differential is a relatively constant factor that 

 varies not at all or at least to a very limited extent in the same 

 individual after the animal has reached the age, when it is able to 

 obtain its nourishment independently of its mother. Such condi- 

 tions as pregnancy, temporary undernourishment, certain infec- 

 tions do not suspend the function of the individuality differential. 

 In addition we could show in a separate series of experiments 

 that particularly those changes which call -^orth compensatorv 

 hypertrophy in the thyroid gland do not noticeably interfere with 

 the reaction against the homoiodifferential. The lymphocytes 

 may invade in enormous numbers the gland even after it has 

 become hypertrophic and again in the end they succeed in de- 

 stroying it. 



THE EFFECT OF HOMOIOTOXINS ON OTHER GROWTH PROCESSES. 



While thus compensatory hypertrophy does not noticeably 

 modify the action of the homoiotoxins, the homoiotoxins may 

 on the other hand, as our recent experiments have shown, to 

 some extent interfere with the development of compensatory 

 hypertrophy of the thyroid gland, not only by bringing about the 

 destruction of the gland, but apparently also by diminishing the 

 frequency of the hypertrophic changes. In a similar manner 

 our previous experiments had shown that homoiotoxins may to 

 some extent interfere with the production of the maternal placenta 

 and the placentomata such as they can be produced experimentally 

 in the normal as well as in the homoiotransplanted uterus. After 

 homoio-transplantation the experimental formation of placenta is 

 diminished. The homoiotoxins interfere, therefore, to some ex- 

 tent not only with purely regulative processes such as occur after 

 transplantation of organs, but also with those changes which lead 

 to compensatory hypertrophy and to placenta formation. They 

 evidently have an injurious influence on a variety of growth 

 processes, and diminish the intensity of those tissue reactions 

 which initiate placenta formation. 



