864 



THE CARCINOGENIC STIMULUS 



II 



Fig. 60. Subcutaneous transplants of a mouse lymphosarcoma. The animal on the left 

 has bi-lateral transplants (t) which were made simultaneously. The mouse on the right also 

 received two transplants, but the second was made ten days after the first. This mouse 

 developed an immune reaction as evidenced by the resistance of the second transplant 

 made into the right side. Immune reactions of this type have been demonstrated against 

 transplanted but not spontaneous mouse neoplasms. 



Fig. 61. Transplant of thyroid tissue (t) into the ear of a mouse. This tissue was hyperplastic 

 thyroid from a mouse fed thiouracil. Such transplants grew only in hypothyroid histocom- 



Legends continued on p. 865 



