MARIAN IRWIN 211 



with this length of exposure these movements remained practically 

 normal. The measurements of the breathing movements were made 

 by determining the length of the time necessary to count twenty 

 movements. In general the normal mouth movements were about 

 twenty in 11 seconds. On comparing Curves A and B, Fig. 1, it is 

 evident that at these concentrations the decrease in CO2 output is 



Bate ^ 



100 yj^^y X 



% 



50- 







Fig. 1. Curves showing the effect of ether upon the rate of CO2 production 

 (Curve B) and the rate of mouth movement (Curve A) of frog tadpoles. The 

 normal rate is taken as 100 per cent in each case. The time of exposure to ether 

 was 150 seconds. Average of six experiments. Probable error less than 2.5 

 per cent of the mean. The figures expressing the per cent of ether should be cor- 

 rected by multiplying by 0.73. 



not due to the decrease in the water supply to the gill system. A 

 quantitative measurement of the body movement was not possible 

 for the reason that the movements of the tail were in many cases 

 too rapid for accurate measurement. However, it may be stated 

 that there was no appreciable decrease in the rate of the body move- 

 ment at the concentrations in which the retardation of the CIO2 

 output took place. Thus, in general it may be stated that the de- 



