No. 581] GERM CELLS AND SOMATIC CELLS 289 



to transplant the connective tissue cells of a rat sarcoma 

 through forty successive generations of animals, and it 

 was merely the result of accidental bacterial infection 

 due to the unfavorable conditions under which the work 

 had to be carried out which caused the ultimate death of 

 the propagated cells. 



An epithelial tumor found by Jensen in a mouse has 

 been propagated in various laboratories through a period 

 of almost fifteen years, and another epithelial tumor of 

 the mouse we have been propagating in mice for a period 

 of seven or eight years, without any sign of diminishing 

 vitality in the propagated cells being noticeable. 



In all these transplantations of tumor cells, be they of 

 connective tissue or epithelial origin, it could be shown 

 that the peripheral cells remain alive and from these sur- 

 viving cells the cell growth starts. These observations 

 suggested to me in 1901 the conclusion that tumor cells 

 may have a potential immortality in a similar manner as 

 germ cells, 5 and inasmuch as tumor cells are only modified 

 somatic cells, I furthermore concluded that the same 

 statement holds good in the case of somatic cells. 5 Fur- 

 ther experiences in the field of experimental tumor inves- 

 tigation during the following years confirmed this conclu- 

 sion and permitted its enunciation with greater definitive- 

 ness. 6 The potential immortality of the somatic cells of 

 course can only be made probable, it can never be defi- 

 nitely proved, inasmuch as our experience merely deals 

 with finite periods. But the same restriction holds good 

 in the case of the germ cells in which the potential immor- 

 tality is likewise merely a strong probability and not a 

 definitely proven fact. 



Weismann believed that protozoa are in the same sense 

 potentially immortal as germ cells, in contradistinction to 

 somatic cells which do not possess potential immortality. 

 Some facts were, however, discovered which, according to 



5 "On the Transplantation of Tumors," Jour. Medical Bescarch, Vol. VI, 

 No. 1, 1901, p. 28; Virchow's Archiv, Bd. 167, 1902, p. 175. 



""Tumor Growth and Tissue Growth," Am. Philosophical Society, 

 XLVII, 1908, and at other places. 



