LIGHT REACTIONS — METABOLISM MAY-FLY NYMPHS 443 



experiments, they were found to be stimulated by the treatment 

 (table 9). 



Two instances of the reversal of positive animals by acid treat- 

 ment are given in the first two columns of chart 4, p. 450. In 

 both instances shown the reversals are typical in that they are 

 very marked and occur almost directly upon the start of acid 

 treatment. In the second instance shown the experimental dish 

 was twice turned end for end and each time the nymph moved 

 directly negative. 



Here we have the same reagent making negative animals posi- 

 tive by either stimulating or depressing them and making positive 

 animals of the same species negative by stimulating them. 



3. Negative vs. positive nymphs; both treated with HCl 



The treatment with hydrochloric acid did not cause all the 

 n5^mphs to reverse their light reactions. When animals that had 

 been made positive were compared with those still negative, it 

 was found (table 10) that the former had a higher rate of carbon 

 dioxide production when the time of exposure had been approxi- 

 mately the same for both nymphs compared. Almost all the 

 nymphs tested came from the preliminary period of stimulation. 

 Theoretically, nymphs long exposed to acid and positive would 

 give less carbon dioxide than those more recently placed in the 

 acid and still negative. This possibility was not tested, since the 

 results can easily be interpolated from the tests given in pre- 

 vious tables. 



Chart 2 Showing graphically the light reactions of four njonphs treated 

 with N/25 HCl and their carbon dioxide production as compared with that of 

 their control nymphs. Column 1 shows two reversals with the acid treatment, 

 the first of which occurred within three minutes. The reversals shown in column 

 1 and that in column 4 were accompanied by stimulation. On the other 

 hand, the reversal shown in column 5, which came after twenty-three minutes' 

 exposure to the acid and which was allowed to remain positive for thirty-five 

 minutes before testing, showed depression. The preliminary test in columns 5 

 and 6 is not charted, but was essentially like the first eight minutes shown. It 

 will be noted that in this test the control became positive due to exposure to light 

 and was therefore more stimulated than the ordinary negative control. Other 

 tests show depression by treatment with acid for this length of time when com- 

 pared with negative nymphs. 



