GROWTH 261 



(1928) exposed bacteria to X-rays and observed that a cell could be 

 killed by being hit by one electron, but only if it was hit in a definite 

 part of the cell which he called the sensitive zone. WyckofT (1930) 

 computed the volume of this zone from experiments with X-rays 

 of various wave lengths and found it to be not more than one- 

 hundredth of the cell volume. Nothing can be said about the form 

 or distribution of this sensitive zone in the cell, but the fact of its 

 existence suggests strongly a special segregation of the growth 

 function corresponding to the chromosomes of larger cells. 



Arrangement of Molecules in the Cell. — A computa- 

 tion of the ^ intensity of energy" or the ^'potential of 

 energy" will permit us a further insight into the rela- 

 tion between the assimilative and the dissimilative 

 mechanism. 



It has just been mentioned that the average cell of 

 Strept. lactis will ferment about 12 X 10~^^ mg. of glucose 

 per hour. The heat liberated in the lactic fermentation 

 of 1 gm. glucose is 82 calories (p. 23). The sugar 

 fermented by a single cell produces 12 X 10~^° X 82 X 

 10-3 = 984 X 10-12 calories. Taking the weight of this 

 cell to be 5 X 10"^^ mg., the energy liberated in one hour 

 is sufficient to heat the cell to 200°C. Considering the 

 enormous surface (about 60 square centimeters per mg. 

 of moist cells, p. 397), radiation and conduction must 

 play a great part in relieving the cell of this amount of 

 surplus energy. Possibly, the energy in the cell is not 

 liberated in the form of heat, but in some other, more 

 harmless form. 



If the entire cell assumed a higher uniform temper- 

 ature, there would be no potential inside the cell. In 

 order to get a conception of the possible energy potentials 

 within the cell, the heat produced per molecule of sugar 

 fermented must be calculated. 



A single glucose molecule weighing a ^ ^r)23 S^-y ^^ 



