CONDITIONS OF CELLULAR IMMORTALITY 65 



we drew, therefore, on the basis of these experiments, the conclusion that 

 ordinary tissue cells are potentially immortal; notwithstanding the fact 

 that, especially under Weismann's influence, the opposite view had been 

 generally accepted, and as it seems to us, with full justification, inasmuch 

 as no facts were known at that time which suggested the immortality 

 of somatic cells. It was the apparently endless transplantation of tumor 

 cells which proved the contrary view. 



"To recapitulate what we stated above : tumors are merely transformed 

 tissue cells. All or the large majority of adult tissues are potential tumor 

 cells. Tumor cells have been shown experimentally to be potentially im- 

 mortal, therefore tissue cells are potentially immortal. 



" This wider conclusion I expressed nineteen years ago. Quite recently, 

 the immortality of certain connective tissue cells has been demonstrated 

 by Carrel through in vitro culture of these cells. Under those conditions 

 the tissue cells escape the mechanisms of attack to which the homoiotoxins 

 expose the ordinary tissue cells in other individuals of the same species. 

 Under these conditions the reactions of the host tissue ag;ainst homoiotoxins 

 which would have taken place in vivo, are eliminated. We must, however, 

 keep in mind that this method of proving the immortality of somatic cells 

 applies only to one particular, very favorable kind of cells; and it is very 

 doubtful, if, by cultivation in vitro, the same proof could be equally well 

 supplied in the case of other tissues. On the basis of tumor transplanta- 

 tions, on the contrary, we were able to show that a considerable variety, 

 perhaps the large majority of all tissue cells possess potential immortality." 



To Loeb unquestionably belongs the credit for first 

 perceiving that death was not a necessary inherent con- 

 sequence of life in the somatic cell, and demonstrating by 

 actual experiments that somatic cells could, under cer- 

 tain conditions, go on living indefinitely. 



Before turning to the next phase of our discussion, 

 let us summarize the ground we have covered up to this 

 point. We have seen that by appropriate control of 

 conditions, it is possible to prolong the life of cells and 

 tissues far beyond the limits of longevity to which they 

 would attain if they remained in the multicellular body 

 from which they came. This is true of a wide variety 

 of cells and tissues differentiated in various ways. In- 

 deed, the range of facts which have been ascertained 



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