GRAFTING 437 



knowledge of the nature and cause of tumors. Being 

 unable to apply the cultivation methods with success, 

 and still expecting to find an infectious agent by which 

 to account for these formations, they made many series 

 of experiments by implanting fragments of tumors 

 derived from human beings into various tissues and 

 cavities of the lower animals. The literature upon 

 the subject is large and, when, reviewed, shows that 

 great ingenuity and the utmost precaution have been 

 employed that the implantations should be made under 

 the most favorable conditions. Shattuck and Ballance, 

 in order that nothing might be neglected that would 

 contribute to success, even went to the length of intro- 

 ducing entire human mammary carcinomas (cancers) 

 into the abdominal cavities of sheep and other animals. 

 In every case, irrespective of the precautions, such tumor 

 transplantations failed, and the conclusion was about 

 reached that no tumor tissue of any kind could be suc- 

 cessfully transplanted, when Hanau, in Weigert's labo- 

 ratory, came into possession of a rat with a squamous 

 cell carcinoma of the vulva, which he transplanted to 

 other rats. To his and everybody's surprise these 

 grafts grew, developed into tumors, behaved like spon- 

 taneous tumors, and caused the formation of metastatic 

 tumor nodules in the lymph nodes. The experiment 

 was for a long time conspicuous because of its exceptional 

 results; then Jensen transplanted a tumor of a white 

 mouse to other white mice, and was successful. The so- 

 lution of the problem was eventually found in the homol- 

 ogous and heterologous nature of the transplantations. 

 Heterologous grafting results in the disappearance of 

 the graft by absorption; homologous grafting trans- 

 plantation of the tissue to other animals of the same 

 kind may be successful, and many investigators in dif- 

 ferent parts of the world have since been able to achieve 

 and continue the homologous transplantation of mouse 

 and rat tumors for indefinite lengths of time through 

 hundreds of generations. When heterologous trans- 



