EXPERIMENTAL ANALYSIS 



not be in some way under the influence of other components of the cell. 

 On the other hand, each element of the cell possesses a considerable 

 degree of independence and stability.' (Claude^^"). Each stimulus and 

 reaction must be fitted into the dynamic pattern of complex trans- 

 mutations which makes up the life of the cell. To find out exactly what 

 changes in this pattern lead to the process of mitosis and how these 

 changes are brought about is the task for the imaginative insight of 

 the biochemist — for still, 'even now those who think in terms of mole- 

 cular events may have visions of progress denied to those whose thought 

 is guided by the visible alone' (Hopkins^^^). 



INHIBITORY studies ON MITOSIS 



In this section, it is proposed to review some of the literature on the 

 effects of chemical substances upon dividing cells. A very large number 

 of papers relate to this subject, but many of them are studies which are 

 primarily concerned with medical or agricultural problems. With the 

 development of chemotherapeutical research in recent years, there 

 has been a considerable increase in the number and complexity of the 

 organic compounds which have been tested on growing tissues, though 

 much of this work relates more to the toxicology of these substances 

 than to the physiology of the dividing cell. 



Each line of inquiry tends to develop its own body of theories and 

 ideas into which fresh information is incorporated ; not always has each 

 school of thought been ready to admit the validity of the results and 

 conceptions of the other. A brief reference to some of the main branches 

 of research may be made. The chief school of research which uses the 

 whole animal, usually the mouse, as experimental material is that of 

 A. P. and P. Dustin and their collaborators, which has been studying 

 for over 25 years the effect of injected substances on the main sites of 

 cell division in the animal. Reviews on the work of this school have been 

 given by Dustin (P.).^^^ ^^^ The chief limitation of this type of research 

 is that in sectioned tissues of the experimental animals there are seen 

 only the end results of the reaction of the cell to the agent, the detailed 

 course of which can only be inferred. Dustin has made the distinction 

 between substances which inhibit the m'totic spindle and those which 

 affect mainly the chromosomes; the latter type of agent has been termed 

 'radiomimetic', since ionizing radiations have an apparently similar 

 effect. The cell is believed to be specially sensitive to the action of such 

 substances when it is about to enter prophase. Not always, however, do 

 different types of dividing cell react in the same way to mitotic poisons, 

 and the distinction between Dustin's two categories is not invariably 

 maintained. 



The analogy with the effect of radiation has been enhanced by the 



183 



