182 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



to explain the special advantage which the eye offers for the growth of certain 

 transplanted tumors, as compared with the subcutaneous tissue or other sites. 

 Against such an interpretation are the recent experiments of Greene, as well 

 as those of Cheever and Morgan, which indicate that a transmission of im- 

 mune processes may take place between the aqueous humor of the eye and the 

 circulating blood, although again, the results of these investigators, working 

 with different types of tumors, differ as to the degree to which such an ex- 

 change may occur. Moreover, as Greene points out, the growth of tumors is 

 enhanced if the testicle is used as the site of transplantation, and in this organ 

 such a barrier between blood and organ constituents does not, in all proba- 

 bility, exist. Also, in other kinds of transplantations the testicle has been 

 found to be a favorable site ; thus, according to Stockard, homoiotranspJanta- 

 tion of the ovary in the salamander Diemyctylus, succeeds only in the testicle ; 

 likewise, the Pearce-Brown rabbit tumor is advantageously propagated by 

 grafting it into the testicle. The most probable conclusion in regard to im- 

 mune substances, at the present time, seems to be that a certain degree of 

 interference with the exchange of these substances between blood and the 

 fluids of the eye may play some part in favoring the growth of tumors in the 

 anterior chamber of the eye, but it may not be the only factor concerned. 

 However, it is possible also that the primary homoio- and heterotoxic sub- 

 stances may pass only with greater difficulty from the circulating blood or 

 lymph into the fluid of the anterior chamber, and that this condition may 

 contribute to the advantage which transplantation of tumors into the eye has 

 as compared to the subcutaneous tissue; furthermore, fluid in this site sur- 

 rounds a part of the periphery of the transplant and this may favor a continu- 

 ous removal of individuality differential substances functioning as homoio- 

 or heterotoxins, from the transplant. But, as stated, there exists the further 

 possibility that still other, as yet unknown, factors may cause a mitigation of 

 the injurious reaction of the host against transplants in special locations, in- 

 cluding the anterior chamber of the eye. 



Transplantations into the eye have contributed additional information as to 

 the effect of hormones on the survival and growth of transplanted endocrine 

 organs. By means of these transplantations, more evidence has been obtained 

 for the conclusion that various secreting cells living under unfavorable con- 

 ditions, may not be able to sustain themselves without receiving stimulation 

 by specific hormones; a certain degree of disharmony between the individu- 

 ality differentials of host and transplant may be one of these unfavorable con- 

 ditions. Strange individuality differentials bringing about degenerative effects 

 in the transplant, as, for instance, in the ovary and adrenal cortex may help 

 to induce connective tissue cells as well as lymphocytes to react very strongly 

 against tissues bearing these strange individuality differentials, in the man- 

 ner already indicated in the discussion of transplantations of ovary and 

 adrenal gland in the mouse. By inhibiting or preventing these degenerative 

 alterations, hormones may protect the transplanted tissues against these in- 

 tensified reactions, especially of lymphocytes. It has likewise been shown 

 that the activity of the connective tissue providing the stroma of organs is 



