260 HARTLEY H. T. JACKSON 



tween the chemicals used and the reactions. Some potassium 

 salts produced a change in the phototaxis of the animals, other 

 potassium salts did not; some acids produced a change in the 

 phototaxis, others did not. It is the same with the alkalies; 

 ammonium hydroxide causes all the animals to become posi- 

 tive immediately when they are dropped into a solution of 

 .0075 per cent, but when the animals are put into a solution of 

 potassium hydroxide, or sodium hydroxide, or potassium carbonate 

 of any concentration which will not kill them outright, there is 

 no change in their phototactic response; they still remain 

 negative. Loeb 2 claims that in all probability light produces 

 chemical changes in the eye or skin of the animals, and that 

 these changes are responsible for the phototactic reactions. If 

 this be true, it might seem not improbable that some definite 

 relation would be found between the classes of chemicals em- 

 ployed and the reaction, but such experiments as have thus far 

 been made tend to prove that no such relation exists. 



In endeavoring to test more thoroughly the effects of chemicals 

 upon phototaxis, experiments were conducted in the dark room, 

 the source of light being an electric tungsten bulb of 350 candle- 

 meters intensity. Seven chemicals were used, namely, ethyl 

 alcohol, ammonium hydroxide, and hydrochloric, nitric, acetic, 

 picric, and chromic acids. I first determined the lowest per cent 

 solution of each of these chemicals which would cause a reversal 

 in the phototactic reaction of the Hyalellas; in other words, the 

 least per cent solution which would make them positive when 

 they were dropped directly into it. I found that ethyl alcohol of 

 .074 per cent, ammonium hydroxide of .0075 per cent, hydrochloric 

 acid of .0067 per cent, nitric acid of .0053 per cent, acetic 

 acid of .01 per cent, picric acid of .0053 per cent, and chromic 

 acid of .0046 per cent would produce this result. In each of these 

 cases, all or nearly all the animals would be in the positive end 

 of the dish making frantic efforts to get nearer the source of light. 

 My next experiment was to place several of the animals in an 

 oblong glass dish, four inches long and one and one-half inches 



2 Loeb, J. Comparative Physiology of the Brain and Comparative Psychology. 

 New York, 1900, and I.e. 



