Chapter 22 



The Nature of the Individuality Differentials and 



of the Reaction of an Organism Against a 



Strange Individuality Differential 



We have discussed the reactions of the host against the various 

 types of individuality differentials in various species of animals, 

 but in every case we have dealt with reactions against tissues con- 

 taining an individuality differential mixed with other substances, and not 

 with the reaction of cells and tissues against an individuality differential 

 isolated in a pure state. No direct attempt has been made so far to determine 

 the chemical structure of this substance. However, by subjecting the tissues 

 to various procedures, it has been possible to draw certain general conclusions 

 as to the chemical constitution of the individuality differentials. We have used 

 for this purpose (1) the effect of graded exposure of tissues to higher 

 temperatures, and (2) the effect of different chemical substances on the 

 individuality differentials present in various tissues. Tissues thus treated 

 were then tested by means of transplantation into different types of hosts 

 in the same way as normal tissues. 



(1) The effect of heat on the organismal differentials in (a) homoiogenous 

 and (b) heterogenous tissues. In experiments by Siebert, to which we have 

 referred already, it was shown that by in vitro exposure of thyroid and 

 cartilage of the guinea pig to temperatures varying between 43 and 51 °C 

 for half an hour and then by transplantation of these pieces into homoiogenous 

 animals, it is possible to diminish very much the lymphocytic reaction 

 of the host against the transplants. These results indicate that the heating 

 at very moderate temperatures reduced markedly the quantity of homoiogenous 

 individuality differentials which diffused from the graft into the surrounding 

 host tissue. It is not certain whether in this case a definite injury of the 

 individuality differentials had taken place in the transplanted tissues, or 

 whether merely the diffusion of these differential substances into the sur- 

 rounding tissue had been made more difficult. 



It is more probable that the first explanation is the correct one, because a 

 short delay in diffusion should not have affected so much the strength of 

 the lymphocytic reaction, but should only have delayed its appearance for a 

 short time. The heating of the tissues at the same temperature affected the 

 reactions of a heterogenous host much less than those of a homoiogenous 

 host; in the former there was only a slight diminution in the number of 

 polymorphonuclear leucocytes and lymphocytes. This effect must have been 

 due to a not very marked injury inflicted on the heterogenous differentials 



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