1913.] Rays upon the Cells of Jensen's Rat Sarcoma. 489 



tumour contains numerous very large sarcoma cells, a few of which are multi- 

 nucleated ; they are not found in the actively growing tumours. Cells of this 

 kind have been described by Clunet* and others as occurring in tumours 

 which have been irradiated in vivo. 



The histological changes indicate that after a long period of irradiation the 

 cells of the growth are killed and are rapidly absorbed. With shorter periods 

 of irradiation, even in cases where no tumour develops, the cells remain at 

 the site of inoculation for a long time, but their capacity for proliferation is 

 diminished. This inability to proliferate is not due, as in immune animals, to 

 failure of the connective tissue to vascularise the graft, but is due to some 

 change in the cells themselves. 



Conclusions. 



1. Jensen rat sarcoma when exposed in vitro to the /3-rays from a source of 

 radium of intensity T63 mgrm. per square centimetre for 90 minutes, or to 

 radium emanation of concentration 0'53 millicurie per cubic centimetre for 

 45 minutes, will not grow upon inoculation into normal rats. 



2. The sarcoma cells which have been irradiated may remain in the animal 

 body for more than 60 days before giving evidence of growth. 



3. Histological evidence shows that failure of the irradiated sarcoma cells 

 to produce a tumour does not necessarily indicate their destruction at the 

 time of inoculation. 



* Clunet, ' Tumeurs Maligues,' 1910. 



