HAROLD P. RUSCH 



Figure 1 is a diagrammatic representation of an unfer- 

 tilized ovum containing symbols which represent these two 

 chief cellular functions together with the cell food necessary for 

 such activity. This representation has been reduced to the very 

 simplest terms. Potential mechanisms for cellular reduplication 

 are represented by a hollow square, and potential mechanisms 

 for specialized cellular functions are shown by hollow circles. 

 The numerous specialized functions of the cell have been reduced 

 to four, each represented by a circle, which may represent a 

 single enzymatic reaction or a series of integrated metabolic 

 processes ; but, since cellular reduplication is basically similar in 



UNFERTILIZED OVUM 



D-MECHANISM FOR CELLULAR 



REDUPLICATION 

 O -MECHANISM FOR SPECIAL 

 FUNCTIONS 

 iI-CELL-FOOD 



Figure 1. 



all cells, only one square is used. The short straight bars ar- 

 ranged at random at one side of the cell represent the cell food 

 or nutrients, also frequently referred to in the literature as 

 building blocks, precursors, or substrates. Although it is 

 tempting to indicate whether the various mechanisms are nu- 

 clear or cytoplasmic, no implications are here intended. 



The term cellular reduplication is preferred, because there 

 can be no mistake about its meaning; but the terms cellular 

 division, proliferation, and "growth" are also used. Growth is 

 the least desirable term because of its broad meaning, but it has 

 the advantage of brevity. 



Figure 2 illustrates the sequence of events associated with the 

 "growth" and differentiation of normal cells. Cells with the 

 most specialized functions are shown at the right, and the 



682 



