4 LORANDE LOSS WOODRUFF 



which brings about again the Kernplasma-Spannung which is the 

 inciting cause of the succeeding bipartition of the cell. 



In a word, some investigations seem to show that there is for 

 each kind of cell a characteristic size relation between nucleus 

 and cytoplasm — variations from which lead to various phenomena, 

 normal and abnormal. Minot holds that a decrease of nuclear 

 as compared with cytoplasmic material leads to a slowing of the 

 division rate, while Hertwig and his school believe that an in- 

 crease of nuclear as compared with cytoplasmic material leads 

 to a slowing of the rate of division. 



Child ('10), from interesting experiments upon senescence and 

 rejuvenescence in a planarian, puts emphasis on physiological 

 rather than inorphological factors as the fundamental cause of 

 these phenomena. 



senescence in nature consists physiologically in a de- 

 crease in the rate of metabolism and this is determined morphologically 

 by the accumulations in the cells of structural obstacles to metabolism, 

 e.g., decrease in permeabihty, increase in density, accumulation of 

 relatively inactive substances, etc. Rejuvenescence consists physiologi- 

 cally in an increase in the rate of metabolism and is brought about in 

 nature by the removal in one wa^^ or another of the structural obstacles 

 to metabolism. 



Conklin ('12) has recently extensively reviewed the subject of 

 cell size and nuclear size on the basis of studies on gasteropods 

 from the standpoint of cell-lineage, and he states: 



My observations do not support the view that senescence is due to 

 a decrease (Minot) or an increase (Hertwig) of nuclear, as compared 

 with protoplasmic material; nor that rejuvenescence is accomplished 

 during cleavage by the great increase, of nuclear material relative to 

 the protoplasm. On the other hand senescence seems to be associated 

 with a decrease, rejuvenescence with an increase of metabolism (Child). 



In a sense there are two aspects of the nucleo-cytoplasmic re- 

 lation theory. One considers the nuclear-cytoplasmic relation 

 during the various phases of the life of the individual cell and its 

 fluctuations during vegetative and reproductive phases. The 

 other takes into account the general nuclear-cytoplasmic rela- 

 tion which obtains in the various cell generations in the life 

 history of an organism, all the cells of which are lineal descendants 

 of a single cell — the fertihzed egg (Metazoa) or exconjugant 



