TISSUE CULTURE 73 



The fact which impresses one most forcibly and which is of 

 the deepest biological significance is the sustained vitality of the 

 cells. Today, after twenty-three years of growth and possibly 

 over 4,000 divisions, prohferation is as active as it was at the 

 beginning. The rate of growth is undiminished, unaffected by 

 time. Life is immortal, but only in a sense, which, when we 

 analyze it, becomes commonplace. In the case of the tissue 

 cultures it is immortal only under the favorable conditions 

 existing in carefully controlled cultures. The life of cells in 

 tissue culture is immortal only because there is survival but not of 

 the original cell. Its progeny have survived, and this is true 



t 



Fig. 57. — Cells from the original "old strain" of Carrel started in 1912 (upper 

 cell dividing with chromosomes at center). At this time the culture was thirteen 

 years old (stained preparation) : X 1000. 



throughout nature. The life of man is immortal in that it 

 survives through its progeny. Weismann enunciated this 

 fundamental principle early in modern experimental biology 

 when he stated that the Protozoa are immortal. The technique 

 of tissue culture has produced nothing new from this point of 

 view, but it has made it possible to keep a strain of somatic 

 (body) cells alive in a manner not heretofore accomplished. 



The embryonic chick cells cared for by Carrel and his associ- 

 ates have, through their progeny, grown for twenty-three years. 

 It must, therefore, be granted that any and every normal living 

 cell possesses these same immortal potentialities, but it is quite 

 evident that a special environment is necessary, an environment 

 which embryonic cells possess but which becomes altered with 

 the attaining of mature age. What has the adult animal acquired 

 or lost which causes the cells of the body to age, to lose the vitality 

 of youth? Through tissue culture we have one answer to this 



