MATILDA M. BROOKS 



199 



The great increase in respiration in 7.3 per cent ether in tap water 

 raises the question whether the bacteria were injured. To obtain 

 some Hght on this question, the contents of. each tube were tested 

 (after an exposure to ether lasting 20 minutes) by plating the bacteria 

 on Petri plates and counting the colonies. Two loopfuls of solution 

 from each Pyrex tube were diluted in 10 cc. of sterile water and from 



RATE 



Fig. 4. Curves showing the effect of various concentrations of ether on the 

 rate of respiration of B. subtilis in tap water (Curve 1) and in 0.85 per cent NaCl 

 (Curve 2). The normal rate (which is taken as 100 per cent) corresponds to 

 a change from pH 8.3 to 8.1 in 5 minutes. Average of three experiments. 



The figures expressing the per cent of ether should be corrected by multiplying 

 by 0.73. 



these, one loopful was placed in 10 cc. of agar-agar and plates were 

 poured in triplicate. These plates were incubated over night at 37°C. 

 and counted the next day. The results were expressed as per cents 

 of the normal. These per cents are plotted as ordinates in Fig. 5 

 and the concentrations of ether as abscissae. In performing this 

 experiment all precautions were observed to ensure sterility of the 

 media. 



