484 STUDIES IN GENERAL PHYSIOLOGY 



dimensions of the molecules in the living cell which are 

 sensitive to light. With these possibilities in view I have 

 undertaken at this time more accurate experiments on the 

 heliotropic activity of the different rays of the spectrum. 

 My previous experiments in this direction were made in the 

 i main with colored screens, which 



O {-) sufficed for the immediate pur- 



i _ pose before me at that time, 



namely, to show that the phe- 



FIG> 138 nomena of animal heliotropism 



are identical with those of plant heliotropism. The latter 

 had also in the main been analyzed only by the aid of colored 

 screens. 



2. The experiments which I described in the paper 

 mentioned in the introduction showed, however, clear physi- 

 ological effects. In these experiments I dealt with oscil- 

 latory discharges, and the nerve-muscle preparation was 

 struck by waves the length of which varied in the different 

 experiments between several centimeters and meters. Yet 

 I maintained that the oscillatory nature of the discharges 

 had nothing to do with these physiological effects, but that 

 the contractions of the muscle were dependent upon the 

 mere disappearance of the electrostatic charge from the 

 two spheres of the discharger. It may perhaps be best to 

 review briefly the chief experiments. We used a Toepler- 

 Holtz machine. As the living tissue or indicator in our ex- 

 periments we used two frog's legs with exposed nerves. 

 Both legs were laid as nearly as possible in the same 

 straight line, so that the two free ends of the nerves 

 touched each other. (Fig. 138). In this way a preparation 

 is obtained in which the capacities are distributed symmetri- 

 cally upon both sides. Through this fact my preparation 

 has an advantage over Danilewsky's, who used only one 

 nerve, connected on the one side with the leg, on the other 



