284 A. FRANKLIN SHULL 



ORIGIN OF THE IDEA OF SIGNIFICANCE OF NUCLEAR VOLUME 



The idea that the relative volume of the nucleus, as compared 

 with the volume of the cytosome, is a causal factor in metabolic 

 processes appears to have had its origin in the early observation 

 that large cells have large nuclei, small cells small nuclei. The 

 extent of the surface of contact between the nucleus and the 

 surrounding protoplasm offered a possible explanation of the 

 degree of interaction of these two parts of the cell — an interaction 

 which most authors have regarded as highly important in cell 

 physiology. When it was found that under certain circumstances 

 the relative volumes of nucleus and cytosome vary, the dis- 

 coverers were not slow to seize upon these variations as possible 

 physiological factors. 



Hertwig ('03), to whom is due the chief development of the 

 idea, found, for example, that the relative size of the nucleus in 

 the Protozoa varies in relation to changes in their life-cycle. 

 Actinosphaerium reared under favorable conditions exhibits a 

 gradual increase of nuclear size through a series of generations, at 

 the end of which the former relative size of the nucleus is restored 

 by extrusion of part of the excess chromatin into the cytoplasm. 

 Similar observations were made by Popoff ('08, '09 a) on Fron- 

 tonia, Stylonychia, and Paramecium. Supporting evidence was 

 found in the work of Gerassimow ('02, '05) upon several species 

 of Spirogyra, in which he was able to show that a change in the 

 size of the nucleus leads to a corresponding change in the size of 

 the cell, and that, under favorable conditions, when the relative 

 volume of the nucleus reaches a certain value cell division ensues. 

 Boveri ('03, '05) extended the general idea of a normal size rela- 

 tion between nucleus and cytosome to the metazoa by discovering 

 that in sea-urchin larvae, in which multipolar mitoses produce 

 nuclei containing various numbers of chromosomes, the size of 

 both the nucleus and the cell depends upon the number of chro- 

 mosomes. His measurements indicated that the surface of the 

 nucleus and the volume of the cell are proportional to the number 

 of chromosomes. 



From some of these investigations and others mentioned be- 

 low Hertwig formulated his idea of the significance of relative 



