NATURE OF THE INDIVIDUALITY DIFFERENTIALS 199 



nuclei, may act as ameboid cells and as phagocytes ; they send pseudopods into 

 the foreign material, take small particles of it into their cell-body and if 

 possible digest them, as indicated by the intracellular vacuoles to which they 

 give rise. The cytoplasm of the giant cells may become quite vacuolated and 

 in the end, the latter perish. Small particles of the foreign body, detached 

 from these aggressive cells, may be found also between the connective tissue 

 fibers surrounding the agar or filling the fissure in the agar which they had 

 produced. In certain cases, but not very frequently, also lymphocytes accumu- 

 late round the piece or in its fissures ; they were found more often in rat and 

 guinea pig than in pigeon, although lymphocytes occur in the circulation in 

 larger proportion in birds than in rodents and although they were more numer- 

 ous around and in homoiogenous tissues in the pigeon than in guinea pig or 

 rat. Their presence around foreign bodies is due to non-specific irritations 

 which the foreign material exerts and perhaps to some as yet unknown acci- 

 dental factors. Occasionally also polymorphonuclear leucocytes penetrate, 

 likewise in tree-like fashion, into the agar and dissolve it readily; here they 

 perish after some time and the dissolved material is ultimately replaced by 

 ingrowing connective tissue. It is not certain whether invasion by these leuco- 

 cytes is the result of an accidental infection by bacteria or whether it is due 

 to other factors. If coagulated egg-white instead of agar is implanted into the 

 subcutaneous tissue, the reactions of the host cells are, in principle, the same 

 as with agar ; but on account of the greater hardness of this substance, it is 

 much more difficult for the cells to penetrate it and the reactions, therefore, 

 take place for the most part in the periphery of the egg-white, but, to some 

 extent, cells do invade it. Formation of fibrillar connective tissue capsules 

 around the pieces seems to be relatively the more prominent the harder the 

 material. 



We see, then, that the same elements participate in these reactions against 

 foreign bodies as against living tissues possessing individuality differentials 

 and species differentials. But as stated, the local reactions against foreign 

 bodies do not show the fine gradations in activity of the host cells which the 

 homoiogenous and heterogenous tissues call forth. There is, here, on the 

 whole, a marked rigidity noticeable, although the degree of participation of 

 lymphocytes and polymorphonuclear leucocytes is very irregular and appar- 

 ently due to factors which cannot be foreseen or are unknown, in contrast 

 to the definite orderly manner in which these cells react against the autoge- 

 nous, homoiogenous and heterogenous differentials of living tissues. 



In contrast to these non-living substances and to tissues that have been 

 killed by heat or by chemical substances, living tissues possess individuality 

 and species differentials which call forth definite graded reactions on the part 

 of the host cells and bodyfluids. However, as we have seen, indirectly also the 

 tissue differentials of the grafts may under certain conditions partake in these 

 specific reactions, either intensifying or weakening them. The character of 

 different tissues belonging to the same donor may affect the reaction against 

 strange individuality differentials : ( 1 ) by variations in the amounts of in- 

 dividuality differentials which they give off; (2) by the differences in the 



