LIGHT REACTIONS — METABOLISM — MAY-FLY NYMPHS 441 



The effect of this treatment upon the carbon dioxide produc- 

 tion is shown in table 7, which Hsts all the determinations, and 

 in table 8, which partially analyzes the results listed in the pre- 

 ceding table. 



The biometer tests show that the nymphs were stimulated 

 wh-en first put into the acid and that this period of stimulation 

 lasted approximately fifteen minutes. The time limits varied 

 with different individuals. After this period of stimulation the 

 nymphs were depressed. This gives two periods in the carbon 

 dioxide production corresponding to the two periods in the re- 

 versals by this strength of the acid. 



The tables show that all nymphs were not tested immediately 

 after reversal, but of those whose carbon dioxide production was 

 found within two minutes after reversal and which had been 

 stimulated by the acid the average time of treatment was 13.2 

 minutes. Thirteen of the twenty-five nymphs so tested had 

 reversed within ten minutes after being placed in the hydrochloric 

 acid. On the other hand, the average time of treatment of the 

 animals similarly reversed and measured, but giving more car- 

 bon dioxide in the control than in the acid, was twenty-seven 

 minutes, and seven of the seventeen nymphs reversed after 

 twenty-seven to thirty-seven minutes' treatment. 



From these experiments it appears that either a marked increase 

 or a decrease may accompany phototactic reversals of these 

 nj'mphs when treated with hydrochloric acid. 



2. Effect on positive nymphs 



About 20 per cent of the Heptageninae tested were positive to 

 light when first tested or became positive under the influence of 

 exposure to light for a short time. This positive reaction is much 

 less stable than the usual negative reaction. Of fifteen carefully 

 plotted tests lasting from 15 to 114 minutes, seven, or 47 per cent, 

 showed a change to the usual negative reaction without treatment. 

 In nineteen tests lasting from 1 to 68 minutes seventeen of the 

 nymphs, 89 per cent, were made negative by N/25 hydrochloric 

 acid. IMost of these became negative within the first five min- 

 utes of treatment and, as was to be expected from the preceding 



