M. M. SWANN 



Unfortunately there is almost no direct evidence, and very little indirect evidence, 

 about the effect on cell size of reducing the energy supply. In the case of ordinary 

 somatic cells, either in vivo or in vitro, measurements of cell size have, it is true, been 

 made from time to time (reviewed by Hoffman, 1953). But the difficulty, not to say 

 impossibility, of estimating with any accuracy the volume of irregularly shaped cells, 

 together with the considerable uncertainty about their degree of hydration, makes 

 the measurements of little value in the present instance. In the case of micro- 

 organisms the situation is rather better. Volume can be estimated much more 



1 



D 



ivision 



a 



Growth 



□ 



Maintenance 



Figure 2. Possible arrangements for the apportioning of the 

 cell's energy supply. For explanation, see text, (a) Inhibition 

 leads to increase in cell size; (b) inhibition leads to increase in 

 cell size; (c) inhibition produces no change in cell size; (d) 

 inhibition leads to decrease in cell size. 



accurately, and what is more valuable, the average dry weight of organisms can be 

 determined. 



A search of the literature has not brought to light any work on the effect of partial 

 anaerobiosis or respiratory inhibition on cell size in micro-organisms. It has been 

 found, however, by Pace and Ireland (1945), that raising the oxygen tension increases 

 the oxygen consumption but decreases the size of Tetrahymena. Since increased oxygen 

 consumption presumably means an increased energy supply, the decrease in size is 

 what might be expected from an apportioning of energy of the type earlier deduced 

 and illustrated in Figure ia. It must be remembered however that increased oxygen 

 tension is liable to act as a poison of uncertain effect. 



192 



