THE BIOLOGY OF THE CELL SURFACE 



to account for cells lacking this synchrony, but it implies 

 that they are abnormal. The synchrony of nuclear and 

 cytoplasmic division is an interesting phenomenon but not 

 an essential characteristic of cell-division; instead of being 

 over-emphaeized in theoretical considerations, it needs 

 itself to be explained. 



A theory devised to explain division of the cell-body 

 should also be consonant with the observable phenomena in 

 the cell both whilst living and when properly fixed. Phy- 

 sico-chemical speculations however ingenious when incon- 

 sistent with the observed phenomena lend little to the 

 solution of the problem. Indeed, we shall notice that in 

 the attempt to explain cell-division the ignorance of the 

 actual process and the exaggerated application of physico- 

 chemical knowledge have together erected serious obstacles 

 to a proper understanding and that, as the research on 

 experimental parthenogenesis, so also that on cell-division 

 can be upheld as an example of the danger which inheres in 

 this kind of physico-chemical study. Again it should be 

 emphasized that the first task in the approach to the prob- 

 lem is to learn as thoroughly as possible the normal process 

 which is to be explained. 



Unfortunately, explanations of the mechanism of cell- 

 division have frequently been based on abnormal cell- 

 behavior induced by experimental agents. The chief error 

 in this type of work does not lie in the use of a strong experi- 

 mental means that brings about abnormality; it lies in the 

 fact that the conclusions overlook this result of the treat- 

 ment. Further, it is clear that experiments, in which the 

 cells were weak and abnormal at the outset, can not serve 

 as a basis for the explanation of the normal process. 



For a theory of cell-division, as for any problem in bio- 

 logy, an appreciation of the normal biology of the cells under 

 their natural conditions is imperative. For example, 

 important as the work on vertebrate cells in tissue-culture 



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