177 



There is on an avei'age, 10 hours l)el\veen Iwo succeed- 

 ing divisions of the same cell; in other words, under 

 Lhe experimental conditions and under the conditions ol' 

 growth in the periphery of a culture, a given numher of 

 cells will be doubled after 10 houi's. If the cells were grow- 

 ing in a single layer, conseciuenlly the area of the culture 

 would have increased to its double size after 10 hours. 

 Approximately, it is the same order of magnitude which is 

 obtained by the planimetric measurements of cultures by 

 Carrel and E b e 1 i n g. 



These experiments have brought out one main fact, 

 namelj', that the cell divisions in a given piece of growing 

 tissue in vitro, an old strain of fibroblasts, seem to proceed 

 periodically and exhibit a form of rhythm. It was observed, 

 under the conditions of experiment, in a regularly growing 

 piece of tissue in vitro, that a high percentage of cells 

 divide within a comparatively short time and that there, 

 as well before as also after, is relatively a long period of la- 

 tency. 



It is conceivable to explain the phenomenon as the result 

 of a controlled action from several of the neighbouring 

 cells with which the cells, about to divide, are in direct con- 

 tact. The rhythmic setting in of a large number of cell 

 divisions should according to this denote that the same 

 impulse or principle induces numerous cell divisions in the 

 explanted tissue simultaneously. 



The phenomenon cannot be explained as the result of 

 environmental conditions, because it was found, that single 

 cells, which possessed all the very best conditions for life 

 and multiplication, plasma and embryonic tissue juice, were 

 never found to divide unless in good contact with several 

 other cells. These experiments seem furthermore to indicate, 

 that the growing tissue cells in vitro, are under the control of 

 the neighbouring cells; we are, in other words, dealing with 

 a partial organism and not of independant cell individuals. 



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