CELL-DIVISION 



Cells in the adult body frequently show a sudden and 

 exaggerated burst of division-activity which results in 

 abnormal growth. Thus tumors are built up by riotous 

 cell-proliferation. The malignant tumor, cancer, in this 

 respect is not different from the benign and to this extent 

 any work on cell-division may be of significance for the 

 cancer problem; this, however, does not mean that every 

 work on cell-division in various forms of animals from 

 Amoeba to vertebrate has direct bearing on the problem of 

 cancer, since here malignancy points to a cause lying beyond 

 the facts which can be established for tumors in general, 

 both malignant and benign. 



The germ-cells, eggs and spermatozoa, display the most 

 intense activity of cell-division, especially during their 

 periods of multiplication. A great deal of our information 

 concerning cell-division is derived from the study of these 

 cells particularly in their period of maturation. 



It is not only among multicellular organisms as egg or as 

 adult that cell-division is of consequence; among unicellular 

 animals and plants it is often the sole mode of reproduction. 

 These single-cell forms live for minutes, hours or days as 

 such and then by dividing into two parts bring into being 

 "new" individuals. Or one cell may divide into several 

 parts each of which becomes a "new" individual. 



In the non-living world, substances may divide, and so 

 multiply and also differentiate and grow. But these phe- 

 nomena are quite unlike those exhibited by living things. 

 Cell-division constitutes a fundamental process which is 

 never observed outside the world of living things. And 

 yet, it still lacks an explanation to which biologists agree. 

 It is, moreover, most often incorrectly defined. The reader 

 should understand that in the following pages my main 

 purpose is to derive a definition. Only after having done 

 this shall I offer an explanation of this phenomenon, the 

 division of the cell. 



24Q 



