ARTICLES 615 



relation theory as we now know it is largely due to the in- 

 vestigations carried on by Richard Hertwig and his students. 

 Hertwig (1903) came to the conclusion that in every cell under 

 normal conditions there is a definite relation between the 

 quantity of cytoplasmic and nuclear materials, which he called 

 the " Kernplasmarelation." According to Hertwig, the mag- 

 nitude of the K/P (nucleus/cytoplasm) ratio determines vital 

 processes such as growth, division, senescence, and physio- 

 logical degeneration. The latter, for example, result from an 

 abnormal increase in the ratio (i.e. in the growth of the nucleus) ; 

 and certain rhizopod and ciliate protozoa in which this con- 

 dition was induced by overfeeding either died, or else regained 

 the normal ratio by direct elimination of nuclear material or 

 by conjugation. The intervals between successive divisions 

 were divided by Hertwig into two periods : ( 1 ) a period of 

 " Funktionelle-wachstum " during which the cytoplasm grows 

 more rapidly than the nucleus, leading to an abnormal K/P 

 ratio ; and (2) a period of " Theilungs-wachstum " during which 

 the normal K/P ratio (the " Kernplasma-Norm ") is regained 

 by the rapid growth of the nucleus, and at the end of which 

 cell-division occurs. The end of the period of functional 

 growth, when the K/P ratio is abnormal, is the moment of 

 " Kernplasma-Spannung." Many external and internal con- 

 ditions are supposed to affect the normal K/P ratio. Thus 

 Hertwig found that the ratio was increased if the organisms 

 were subjected to low temperatures, and was diminished at 

 higher temperatures. 



Many investigators have studied the nucleo-cytoplasmic 

 relations in Protozoa and in Metazoa, confirming in part the 

 conclusions reached by Hertwig and his followers. The 

 work of Minot (1908), however, leads to a theory directly 

 opposed to that of Hertwig. Minot finds that in segmenting 

 eggs the amount of nuclear material increases as compared 

 with the quantity of cytoplasm, and concludes that this increase 

 is indicative of the process of rejuvenation. Rejuvenescence 

 is thus revealed as an increase of the nuclear material, and 

 senescence as an increase and differentiation of the cytoplasm. 

 When applied to Protozoa, Minot's theory requires, " in those 

 cells which are old, an increase in the proportion and in the 

 differentiation of the protoplasm (cytoplasm), and consequently 

 a diminution in the relative amount of nucleus " (1908, p. 231). 



The theory offered by Hertwig to account for the various 

 complex processes that occur during the life-cycles of the 

 Protozoa appears at first quite plausible, but will not with- 

 stand close analysis. The data are entirely inadequate to 

 sustain the claims of the theory, but investigations of the 

 actual relations of nucleus, chromatin, and cytoplasm to one 



