Scientific Proceedings. 



(85) 21 



3 (49). " The transformation of negatively heliotropic animals 

 (Gammarus pulex) into positively heliotropic animals by 

 chemical means" : JACQUES LOEB. (Presented by SIMON 

 FLEXNER.) 



After it had been proved that the heliotropism of animals and 

 plants is identical, it seemed desirable to find means by which 

 positively heliotropic animals could be transformed into negatively 

 heliotropic ones, and vice versa. Groom and Loeb found that 

 such a transformation was possible in the nauplii of Balamis per- 

 forates at Naples by the influence of light, inasmuch as these ani- 

 mals were positively heliotropic in very weak light and negatively 

 heliotropic in strong light. 1 Later Loeb found that the marine 

 Copepods and young larvas of Polygordius became positively helio- 

 tropic on lowering the temperature as well as on increasing the 

 concentration of the seawater, while they became negatively helio- 

 tropic under the opposite influences. 2 Moreover Loeb observed 

 that negatively heliotropic Copepods can be made positively helio- 

 tropic by mechanical agitation, 2 and Miss Towle showed that the 

 sign of heliotropism in Cypridopsis can be reversed by contact with 

 solid bodies. 3 Holmes made the discovery that the positively 

 heliotropic terrestrial Amphipods, e. g., Orchestia agilis, become 

 negatively heliotropic when thrown into water. 4 



The author had tried in vain to change the sense of heliotrop- 

 ism in animals by chemical means, and this gap was felt the more 

 keenly, inasmuch as he was led to believe that chemical changes 

 might ultimately determine changes in the sense of heliotropism. 

 Recently, however, the author succeeded in finding instances in 

 which specific chemical substances were capable of transforming 

 the sense of heliotropism in animals. 



The experiments were made with a fresh water shrimp (Gam- 

 marus pidex), which can be obtained at any time in large quantities 

 at Berkeley. If one puts a large number of these animals sud- 

 denly into distilled water or into common tap water, they all be- 

 come at first very negatively heliotropic. It is possible that this 

 is caused by the mechanical agitation, connected with the trans- 



1 Groom and Loeb : Biologisches Centra Iblatl, 1890, p. 160. 



2 Loeb : Pfluger' 's Archiv., 1893, liv, p. 81. 



3 Towle: American Journal of Physiology, 1900, iii, p. 345. 



4 Holmes : Ibid., 1901, v, p. 211. 



