THE BACTERIAL ENDOSPORE 



41 



^^\0a^ 







4 6 8 



Time in hours 



Fig. 2. pH, oxygen demand and residual glucose vs. time. 



the oxygen demand was determined by measuring the rate of 

 disappearance of dissolved oxygen from an aliquot sample of 

 the culture by means of a dropping mercury electrode and a 

 polarograph. By making frequent measurements of the dissolved 

 oxygen content in such a sample, we could plot a curve showing 

 the change in concentration of dissolved oxygen versus time; 

 and the slope of this curve, we considered the measure of the 

 oxygen demand. 



As is apparent from the above, we reached the first peak in 

 the oxygen demand curve at the same time we obtained the 

 minimum in the pH curve. Shortly thereafter, the pH begins to 

 rise and with this rise a very sharp rise m the oxygen demand 

 occurs. A new enzyme system has apparently developed to 

 utilize the acids which are responsible for the lowering of the 

 pH. As these acids are oxidized, a very high demand for dis- 

 solved oxygen develops. In fact, the oxygen demand at this 

 stage far exceeds the oxygen demand during vegetative growth. 

 During this second rise in the oxygen demand curve and the 

 corresponding rise in the pH curve, we began to observe 



References p. 59 



