THE APPLICATION OF QUANTITATIVE STIMULUS 31 



is interposed between A and B, is much more perfect. 

 According to this arrangement, the specimen is tightly 

 clamped in the middle, by which device the excitation of 

 either end is practically precluded from affecting the other. 



Stimulation is brought about by means of torsional 

 vibration. The stem or petiole is fixed, at its middle, in a 

 vice, V, the free ends being held in tubes, c c', each provided 



FIG. 21. Complete Apparatus for Method of Block and Vibratory 

 Stimulation 



Amplitude of vibration which determines the intensity of stimulus is 

 measured by the graduated circle seen to the right. Temperature is 

 regulated by the electric heating coil R. P'or experiments on action 

 of anaesthetics, vapour of chloroform is blown in through the side tube. 



with three clamping jaws. A torsional vibration may now 

 be imparted to the specimen at either end by means of the 

 handles H and H' (fig. 20). The amplitude of vibration 

 which determines the intensity of stimulus can be accurately 

 measured by the graduated circle, and may be predeter- 

 mined by means of the sliding stops S s/ The complete 

 vibrational apparatus, by means of which various experi- 

 mental investigations may be carried out, is given in fig. 21. 



