i66 Viewpoints in the Study of Growth [Jan. 



though it may be exposed to an internal rather than an external 

 medium. One of the secrets of the cessation of growth in higher 

 forms Hes in the hmitation of this cell division. 



A further aspect of the cessation of growth concerns the rela- 

 tions of nucleus to cytoplasm in the growing cellular masses. The 

 functions of nutrition and growth in cells depend upon the presence 

 of a nucleus. Cells which attain a very large size may contain many 

 nuclei. The process of cell division is determined by the ratio of 

 the mass of nuclear chromatin material to that of the protoplasm of 

 the cell. Jacques Loeb has pointed out that after fertilization there 

 is an enormous synthesis of nuclear material. He suggests the pos- 

 sibility that the ratio determining cell division may be determined 

 by the laws of mass action and chemical equilibrium. This syn- 

 thesis of nuclear Compounds from the protoplasmic constituents is 

 a reversible process, according to Loeb. If there are continual 

 readjustments to dispel the disproportion between nuclear and pro- 

 toplasmic material, the cessation of growth may be correlated in 

 some way with the final establishment of equilibrium according to 

 definite chemical laws. 



Abnormalities of growth are attributable to manifold and di- 

 verse causes. Constitutional defects, faulty nutrition, and various 

 environmental factors may be more or less responsible. It is cor- 

 respondingly difficult to classify on an etiological basis the mani- 

 festations which they occasion. There occur deviations which are 

 presumably still within the realm of the normal. This applies, for 

 example, to the variations in the growth of the individuals of a 

 litter, or between different litters. Anomalies of growth expressed 

 by an exaggeratcd rate are among the rarities of physiology. In- 

 stances of early gigantism which might fit this category have been 

 described. The more frequent cases of rapid growth usually rep- 

 resent recovery or response to suppressed growth rather than actual 

 growth de novo. In other words, whenever the growth of an 

 entire organism as well as that of individual organs is modified in 

 the sense of acceleration this usually involves the reversal or return 

 of a morbid condition to the normal. 



Inhibitory features of growth may manifest -themselves by ab- 

 normally diminished growth, untimely complete cessation of growth 

 (Wachstumsstillstand), or even decrease in size. Defects of nutri- 



