THE ACHROMATIC FIGURE, CYTOKINESIS, AND CELL WALL 185 



the electromagnetic field, he concluded that the chromosomes and the 

 cytoplasm carry charges of unlike sign: the daughter centrosomes repel 

 each other and move apart because of their like sign, the spindle poles 

 being of like sign also. The movement of the chromosomes to the poles 

 he held to be due to the combined action of two forces: the mutual repul- 

 sion of the similarly charged daughter chromosomes, and the attraction 

 between the oppositely charged centrosomes and chromosomes. 



The fact that the two centrosomes and hence the two spindle poles 

 are electrically homopolar (Lillie) and alike osmotically at once makes it 

 apparent that the mitotic figure does not represent an ordinary electro- 

 magnetic field, for in the latter the poles are of unlike sign the field is 

 heteropolar. It has consequently been suggested by Prenant (1910) and 

 Hartog (1905, 1914) that the mitotic figure is the seat of a special force, 

 analogous to electrostatic force but not identical with it, which is peculiar 

 to living organisms. This new force they call "mitokinetism." 



A large amount of discussion has centered about the possible role of 

 electrical forces in mitosis, and many kinds of normal and abnormal 

 mitotic phenomena have been cited as evidence for various views. So 

 far as conclusive statements are concerned, there is disappointingly little 

 of a definite nature that can be said. Meek (1913) asserts that the only 

 generalization which is at present possible is the negative one that 

 "the mitotic spindle is not a figure formed entirely by the action of 

 forces at its poles." 



Conclusion. In conclusion we may emphasize the fact that the 

 achromatic figure depends for its operation upon a variety of interacting 

 factors. Certain investigators have doubtless done good service in em- 

 phasizing the importance of one or another of these factors streaming, 

 surface tension, contractility, gelation, electrical phenomena, and the 

 like but it has become increasingly evident that in no one of them alone 

 is the key to the problem of mitosis to be found. In spite of the confi- 

 dence that some progress has been made, at least in the elucidation of 

 certain phenomena which must have a part in any ultimate explanation, 

 it is nevertheless true that the statements made twenty years ago by 

 Wilson (1900, p. Ill) may be taken as an essentially accurate expression 

 of the condition of the subject: "When all is said, we must admit that 

 the mechanism of mitosis in every phase still awaits adequate physio- 

 logical analysis. The suggestive experiments of Biitschli and Heidenhain 

 lead us to hope that a partial solution of the problem may be reached 

 along the lines of physical and chemical experiment. At present we can 

 only admit that none of the conclusions thus far reached, whether by 

 observation or by experiment, are more than the first naive attempts to 

 analyse a group of most complex phenomena of which we have little real 

 understanding." 



