A Rat Tumor. 



53 



tion. The original tumor was of complex histological structure 

 and has been regarded by us as consisting predominantly of a 

 tissue of sarcomatous nature and to a less extent of irregular 

 tubular formations resembling structures seen in certain endo- 

 theliomata. In the fifth generation of one series of transplanta- 

 tions, metastases were first noted in the regional lymphatic glands. 

 In all previous generations the metastases were to the lungs and 

 the kidneys ; and in the other series this change in properties has 

 not been observed. In the succeeding generations between the 

 fifth and the eleventh, of the particular series mentioned, the 

 lymphatic metastases have grown more common and more widely 

 disseminated. Coincident with this change in properties of the 

 tumor, a modification in the histological structure has been noted ; 

 the tumor has become progressively more and more adenomatous 

 in appearance until now it has entirely cleared itself of that part 

 which had been taken to resemble sarcoma. Hence metaplasia of 

 the tumor in the direction of carcinoma has taken place, with which 

 change is associated the acquisition of the property of involving 

 the nearby and distant lymphatic glands in its growth. 



