MATILDA M. BROOKS 201 



Fig. 5 shows that as the concentration of ether increases up to 1.1 

 per cent there is a decrease in rate of growth, reaching a minimum at 

 about 0.95 per cent. Concentrations of ether from 1.1 to 4 per cent 

 produce increase in growth with a maximum at 2.9 per cent. All 

 higher concentrations of ether produce decrease in growth. These 

 observations show that ether is toxic in low concentrations and in very- 

 high concentrations, while intermediate concentrations stimulate 

 growth. 



A possible correlation between Fig. 4 and Fig. 5 may be made. 

 In Fig. 4 there is a steeper ascent in the curve up to 1.1 per cent con- 

 centration of ether, and this corresponds to the first period of toxicity 

 in Fig. 5. Then there follows a more uniform increase in respiration in 

 Fig. 4 corresponding to an increase in growth in Fig. 5. Above 2.9 per 

 cent ether, Fig. 4 shows the very steep ascent of the curve (or very 

 rapid respiration) and Fig. 5 shows a sudden descent "of the curve 

 with a decrease in growth or death of the bacteria. 



SUMMARY. 



1. In all the concentrations of ether studied (from 0.037 to 7.3 per 

 cent) there is an increase in the rate of respiration of Bacillus subtilis 

 followed by a decrease. 



2. In 7.3 per cent ether in tap water there is an extraordinary in- 

 crease in the output of CO2 (amounting to 50 tirnes the normal). 

 This does not occur when 0.85 per cent NaCl is added, which indi- 

 cates antagonism between ether and NaCl. 



3. Ether is toxic in low concentrations (0.037 to 1.1 per cent) and 

 high concentrations (3.65 to 7.3 per cent) but in intermediate con- 

 centrations (1.1 to 3.65 per cent) stimulates growth. 



