434 CHAP. XXXVII. GENERAL REVIEW 



Effect of variation of temperature. — Rise of temperature 

 up to an optimum induces an enhancement of the rate of 

 torsion ; lowering of temperature, on the other hand, brings 

 about a depression or an arrest of movement (p. 388). 

 At the critical temperature of about 60° C. there is a sudden 

 reversal of torsional movement indicative of the spasm of 

 death (p. 390). 



Effect of chemical agents. — The effect of a moderate dose 

 of ether is a very marked enhancement of the rate of 

 torsion. Chloroform causes a preliminary enhancement of 

 the rate of torsion, followed by reversal and arrest of the 

 movement (p. 393). The preliminary effect of poisonous 

 solutions is an enhancement of the rate of torsion, followed 

 by reversal and final abolition of movement (p. 392). 



Effect of Diffuse Stimulation on Autonomous 



Torsion 



Feeble stimulation, whether electric, mechanical or 

 photic, enhances the rate of torsion, whereas strong stimu- 

 lation retards it even to actual reversal (p. 396). 



The effect of indirect stimulation is an enhancement of 

 the rate of torsion (p. 399). 



In regard to photic stimulation, the effect of red light 

 is an enhancement of the rate of torsion, while blue light 

 causes a marked retardation (p. 402). 



Geotropic stimulation. — When the organ is held upside 

 down, the rate of normal torsion undergoes retardation, 

 which may even culminate in the actual reversal of the 

 torsional movement, proving that geotropic stimulation 

 is more effective in the inverted position. Facts have 

 already been adduced which appear to show that the 

 excitability of the ectoplasmic layer is greater at the apical 

 end of the geo-perceptive cell than at the basal end (p. 356). 

 In an inverted position the heavy particles, which are 

 with good reason supposed to cause geotropic excitation, 

 press against the apical ends. The retardation of torsion 



