30 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



In the ovary, the larger-sized follicles and corpora lutea are the most sensi- 

 tive constituents and they are therefore the first ones to be destroyed after 

 transplantation; in other cases, the small-sized follicles survive but do not 

 develop to a larger size if the individuality differentials of host and transplant 

 are not harmonious. Much more resistant than follicles is the germinal epi- 

 thelium, which covers the ovary and usually forms a cyst after transplantation. 

 Likewise, cortical spindle-cell connective tissue and medullary ducts, as well 

 as germinal epithelial ducts, and also the epithelium and unstriated mucosa of 

 the Fallopian tubes are more frequently able to withstand the injurious effects 

 of homoiotoxin than even the small follicles. Most often the tissue remaining 

 after destruction of all the others are strands of smaller and larger cuboidal 

 cells, which are probably derived directly from the interstitial gland, and in- 

 directly from the theca internal cells of atretic follicles ; and these cells may be 

 quite active as phagocytes and thus help in the removal of necrotic or hemor- 

 rhagic material. It may be remarked here that hemorrhages occur in certain 

 transplanted tissues and also in some non-transplanted organs, such as the 

 adrenal gland, probably more often than might be expected. The characteris- 

 tics of the ovary in the mouse, which we have described, make this organ very 

 suitable for the analysis of the individuality differentials. 



Striated muscle tissue is fairly resistant and can be easily transplanted, 

 whereas bone marrow is a rather sensitive organ that readily perishes. In con- 

 trast to ovarian tissue, testicle is sensitive. However, the power of resistance 

 of analogous tissues may differ in different species ; thus it seems that ovarian 

 structures are more suitable for grafting in the rat and mouse than in the 

 guinea pig. Different tissues differ also in their ability to grow after trans- 

 plantation and also in their mode of regeneration, and these growth processes 

 are inhibited by incompatibilities between the individuality differentials of host 

 and transplant. Furthermore, there seem to be some differences in the quan- 

 tity of individuality differential substances produced or given off by various 

 tissues. Those possessing a very active metabolism, such as thyroid, produce 

 these substances apparently in larger quantities than does cartilage. This con- 

 clusion is suggested by the fact that different tissues differ in the readiness 

 with which they attract lymphocytes, and it may be assumed that the accumu- 

 lation of lymphocytes is an indicator of the amount of active individuality 

 differential substances. 



^^r. As to the methods which are most useful in the analysis of the individu- 

 ality differentials, the place of transplantation is important. It is necessary 

 to select a place sufficiently large for the simultaneous insertion of multiple 

 grafts, or, in other cases, for the serial transplantation of pieces of tissue, 

 where, also, these operations can be done without serious interference with the 

 health of the animals and where, moreover, the transplants can be recovered 

 at the time of examination without much difficulty. Pockets in the subcutaneous 

 tissue seem to be most suitable for this purpose, and by using this site in the 

 majority of our experiments we avoided the introduction of unnecessary varia- 

 tions. In making the pocket it is important to avoid hemorrhages, which might 

 interfere with the nourishment of the transplant in the period following opera- 



