132 



SCIENCE 



[N. S. Vol. XXXVIII. No. 969 



of acids, alcohols and esters,' there have been 

 various attempts to bring about a negative 

 reaction by chemical means. It is true that 

 raising the temperature, or the addition of 

 alkalis, tends to break up positive collections 

 of these animals, but such treatment does not 

 cause a negative gathering. Until recently 

 ultra-violet light of wave-length shorter than 

 3,341 A. u. has been the only generally suc- 

 cessful means of artificially causing a nega- 

 tive collection of fresh-water Crustacea.^ But 

 it has lately been shown by Drzewina^ that 

 the larvse of lobsters give such a negative 

 response when treated with potassium cyanide. 



In a former paper it was pointed out that 

 the addition of strychnin to water containing 

 Daphnia destroys the positively phototropic 

 responses of these animals, and that such 

 treatment when applied to Diaptomus causes 

 them to form a strong negative collection. 

 Atropin gives the same result, but to a less 

 marked degree.' 



In order still further to test the effect of 

 alkaloids and other substances upon the light 

 reactions of fresh-water Crustacea, the follow- 

 ing experiments were carried out at the New 

 Monterey laboratory during December, 1912. 

 The material used consisted of Diaptomus 

 hakeri'' taken from the Del Monte lake. The 

 freshly collected animals were put into finger- 

 bowls, each of which contained 25 e.c. of lake 

 water. The preparations were then placed 

 upon a table near the window, but never in 

 direct sunlight. Normally, Diaptomus is in- 

 different to light, the individuals remaining 

 pretty evenly distributed about the dish. But 

 the addition of acids, alcohols or ether always 

 causes the animals in the dish treated to form 

 a dense collection on the window side. In 



' Loeb, J., ' ' Bynamics of Living Matter, ' ' p. 

 131. 



'Loeb, G., Pfl-iiger's Ardiiv, Bd. 115 s.; Moore, 

 A. E., Journ. Exp. Zool., Vol. 13, p. 573. 



' Drzewina, Anna, C. S. Soc. Biol., Vol. 71, p. 

 555. 



* Moore, A. R., Univ. Calif. Publ. Physiology, 

 Vol. 4, p. 185. 



"I am indebted to ProfessoT Kofoid for the 

 identification of this form. 



order to insure" equal concentration of a given 

 substance tiroughout the preparation, the lat- 

 ter was always thoroughly stirred after the 

 addition of the reagent. 



If, now, to a normal preparation there be 

 added 0.6 c.c. of a 1 per cent, solution of caf- 

 fein, in two minutes the animals all collect in 

 a dense cluster on the side of the dish away 

 from the light, i. e., they become negatively 

 phototropic. This collection remains thirty 

 to thirty-five minutes. It was thus possible 

 to observe opposite effects in two dishes of 

 the same material placed side by side, the one 

 with all of the animals forming a dense clus- 

 ter nearest the window (caused by adding the 

 acid), the other with all the animals collected 

 on the side of the dish farthest from the 

 window (caused by adding the caiiein). In 

 either case after the characteristic gathering, 

 if the dish be turned through an angle of 

 180° the Crustacea in it swim back across the 

 dish and re-form, the collection having ihe 

 former position with reference to the light. 

 The addition of 0.05 c.c. of a i per cent, solu- 

 tion of strychnin nitrate to a normal prepara- 

 tion causes all of the animals to become nega- 

 tively phototropic, but does not result in their 

 forming a dense collection as in the case of 

 cafiein. Strychnin, because of its toxicity, 

 causes the Diaptomus treated with it to die 

 within five minutes. It was also found that 

 if 0.5 c.c. of a J per cent, solution of atropin 

 (alkaloidal) be added to a normal preparation 

 of Diaptomus, we obtain much the same result 

 as with strychnin, i. e., a weak negative col- 

 lection. Other alkaloids such as digitalin, pilo- 

 carpin, physostigmin, ricin and cocain, gave 

 no significant results with this form. 



If the Diaptomus were first made positively 

 phototropic by the addition of alcohol or acids, 

 it was found impossible to alter their response 

 by the action of caffein, strychnin or atropin. 

 On the other hand, animals which had formed 

 a negative collection under the influence of 

 caffein, if treated with carbonated water, at 

 once changed their response and, swimming 

 to the light side of the dish, formed a positive 

 gathering. This confirms my former state- 

 ment : 



