HETEROTRANSPLANTATION 119 



homoiotransplanted tissues, the latter, when killed by heating, no longer 

 elicited the typical homoio-reaction. There was a marked lessening of the 

 lymphocytic reaction normally called forth by homoiotransplanted thyroid or 

 cartilage together with the adjoining fat tissue, but again the connective tissue 

 reaction was not markedly diminished in such a thyroid transplant ; it could 

 even be slightly increased. The reaction of the connective tissue is partly 

 directed against necrotic tissue; it is, therefore, not seriously affected by the 

 heating. But, the much more specific lymphocytic reaction in case of homoio- 

 transplantation depends upon the presence of actively metabolizing tissue, 

 because homoiotoxins are produced and given off mainly by functioning 

 homoiogenous tissue. This interpretation is supported also by other observa- 

 tions and experiments, to which we shall refer later. Of interest is also the 

 finding of Siebert, that heating homoiogenous cartilage and perichondrium at 

 47° for 30 minutes seemed to increase the regeneration of cartilage by the 

 perichondrium around necrotic injured cartilage. On the other hand, it might 

 be argued that the heterotoxic action remains almost as strong after heating 

 as it was in the case of unheated tissues, because the exposure to moderate 

 heat did not seriously injure the contaminating bacteria ; but against this 

 interpretation may be cited experiments in which the heterogenous tissues 

 were exposed to the temperature of boiling water. In these experiments, to 

 which we have already referred, the thyroid and cartilage, with adjoining fat 

 tissue, of rats, were boiled for 5 minutes in normal NaCl solution and then 

 transplanted to guinea pigs. In the examination, which took place after 12 

 and 20 days, the reactions were found to be essentially the same as after 

 heterotransplantation of the unboiled tissues, except that in the boiled thyroid 

 the colloid of the acini remained preserved in the grafts, while, as was to be 

 expected, the acinus tissue, as well as cartilage and fat tissue, was necrotic. 

 The essential point in such experiments is that the boiled heterogenous tissues 

 still attracted the polymorphonuclear leucocytes in large numbers, and that the 

 infiltration with the latter was almost as strong as in the transplants of non- 

 boiled rat tissues in the guinea pig ; lymphocytes were in evidence in or around 

 these tissues after 12 days, but they were no longer found after 20 days, 

 although they were seen in the unboiled grafts at this time. It is very difficult 

 to believe that under the conditions of these experiments bacterial infection 

 was the cause of the accumulation of polymorphonuclear leucocytes in cr 

 around the transplants. 



2. In further support of these conclusions, there may be cited experiments 

 carried out by Blumenthal, to which we have already referred. When he 

 transplanted small pieces of autogenous, homoiogenous or heterogenous tis- 

 sues under the skin in various species, changes in the absolute number and 

 distribution of lymphocytes and polymorphonuclear leucocytes took place in 

 the circulating blood, which in principle corresponded to those occurring 

 locally around such transplants. In the case of homoiotransplantation there 

 was an increase in lymphocytes, which began in the first few days following 

 transplantation and reached a maximum between about the third and tenth 

 days. The exact time of the maximum varied with different tissues, according 



