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 
= a main with colored screens, which 
© sufficed for the immediate pur- 
ab ae pose before me at that time, 
Pe eee namely, to show that the phe- 
FIG, 188 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 
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