DISPOSITION OF CHROMOSOMES IN MITOSIS. 195 



I believe, due essentially to a series of relatively simple condi- 

 tions the nature of which I shall attempt to analyze below. 



What then are the conditions that determine the disposition 

 adopted by the chromosomes and the chromatic filament in the 

 dividing cell ? In the prophase of mitosis the chromatin l be- 

 comes disposed in so many cells in the form of one or more 

 elongated deeply staining 2 filaments coiled within the nuclear 

 membrane into a roughly spiral form, that the arrangement is 

 regarded as typical. This is the well-known " spireme " stage. 

 The spireme then segments into the definite number of chro- 

 mosomes characteristic of the cell ; the nuclear membrane dis- 

 appears and the chromosomes are drawn into the equatorial plane 

 of the cell ; here they assume the arrangement known as the 

 " equatorial plate " in which, it is to be noted, a distinct interval 

 separates each chromosome from its neighbors. Each then 

 divides, typically by a process of longitudinal splitting, into the 

 two daughter-chromosomes which recede toward opposite poles 

 of the cell ; here later the daughter-nuclei are reconstituted from 

 the two groups of daughter-chromosomes thus formed. 



Both the adoption of this remarkable spiral arrangement and 

 the manner in which the chromosomes become disposed in the 

 equatorial plate are, I shall attempt to show, dependent mainly 

 upon one simple physical property which the particles of chro- 

 matin possess in common with other similarly charged colloidal 

 particles-- namely, the property of mutual repulsion. It may 

 now be considered as finally established that a colloidal substance 

 in solution is in the condition of a more or less finely divided 

 suspension, each particle of which is at a different electrical po- 

 tential from the adjoining layer of liquid, /. c., carries an electri- 



1 This is the cytological term ; chemically this substance is undoubtedly nucleo- 

 proteid in nature ; the chromosomes are probably similar to sperm- nuclei in their 

 composition, as we may infer from the similarity between the micro-chemical reactions 

 of the two. The nuclein of sperm-heads is relatively simple in composition and 

 contains a large proportion of nucleic acid. For a general account see R. Burian in 

 Asher u. Spiro's Ergebnisse der Physiologic, 3, 1894, I. Abtheilung, Biockemie, pp. 

 48-106. 



2 The increased depth of stain is an indication of increased acidity, /. e., increased 

 liberation of hydrogen ions ; this involves an increase in the electrical negativity of 

 the colloidal substance and consequently in the force with which adjacent portions of 

 the filament repel one another. 



