196 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



through the heating. Blumenthal subsequently tested the effect of heating of 

 both homoiogenous and heterogenous tissues on the organismal differentials 

 by means of white blood cell counts. In these experiments, also, the tissues 

 were exposed to heat for 30 minutes in a test tube previous to transplanta- 

 tion. A temperature of from 45° to 50°C hardly affected the individuality 

 differential of guinea pig or rat thyroid, nor was the individuality differen- 

 tial of pigeon skin, which normally shows a weak reaction, much affected 

 thereby. The same negative result was obtained when rat skin was heated at 

 52°C, but the individuality differential of pigeon thyroid, heated at 54°C, 

 was weakened or destroyed in one-half of the experiments. This temperature 

 seems to represent the critical point ; but if the temperature reached 56°C, 

 the individuality differential of thyroid in various species was destroyed, 

 but that of the guinea pig kidney was merely weakened; presumably the 

 denser texture of the kidney affords a better protection against the effect of 

 the heat. 



To test the heterogenous organismal differentials (species differentials), 

 tissues were exchanged between rat and guinea pig. Heating at 56° C de- 

 stroyed the heterogenous differentials of thyroid tissue of rat and guinea pig, 

 but left those of cartilage and kidney unaffected. In kidney tissue, heating at 

 60°C destroyed the differentials in seven out of eight experiments, and in 

 cartilage this temperature injured or destroyed the differentials in one-half 

 of the cases, but heating at 65°C destroyed also the species differential in 

 cartilage. In the experiments of Siebert, as well as in those of Blumenthal, 

 the heterogenous differentials were somewhat more resistant to heat than 

 the homoiogenous differentials. However, the temperatures needed for the 

 injury of both types of differentials were somewhat lower in the experi- 

 ments of Siebert, who used the local reactions as a test, than in those of 

 Blumenthal, who made use of the blood-cell reaction. Furthermore, in the 

 latter series the tissues possessing a denser texture were more resistant to 

 the destructive effects of heat than those possessing a looser structure. While 

 the differentials in thyroid were more sensitive than those in kidney, the latter 

 were more sensitive than those in cartilage. This again corresponds to the 

 gradation of sensitiveness of the various tissues to the action of strange 

 differentials. The injury of the tissues takes a course parallel to that of the 

 organismal differentials, which they contain. In general, we may conclude 

 that the homoiogenous and heterogenous differentials possess marked sen- 

 sitiveness to the injurious effects of heat, corresponding approximately to the 

 heat sensitiveness of the organs of which they form a part and this sensitive- 

 ness may be attributed to the labile proteins which are the most characteristic 

 constituent of living tissues. It seems probable therefore that the differentials 

 themselves are proteins, or combinations of proteins with certain chemical 

 groups of a different kind. 



This conclusion is supported by experiments in which Blumenthal ex- 

 posed tissues to the action of various chemicals and then tested their effect on 

 homoiogenous differentials by the alterations induced by these differentials in 

 the white blood counts of the host. Least injurious for the individuality differ- 



