EFFECT OF ELECTRIC STIMULATION 



63 



of sensitive protoplasm. This is sometimes facilitated 

 by special anatomical structures such as tactile hairs, by 

 which mechanical stimulus becomes accentuated, and by 

 lens-shaped epidermal cells for focusing the stimulus of light 

 on the protoplasm. 



In regard to the effect of different modes of stimulation 

 on growth, the subjects to be considered in this and sub- 

 sequent chapters are the following : 



1. The Effect of Electric Stimulation. 



2. The Effect of Stimulus of Light. 



3. The Effect of Mechanical Stimulation. 



4. The Effect of Thermal Radiation. 



5. The Effect of Stimulus of Gravity. 



Effect of Electric Stimulation 



A form of stimulation which is extensively used in physio- 

 logical investigations is the electric stimulus of an induction 



h 



\-5 Sr\ 



1 



^ 



UIIII|IIII|III| 



4)0 810 2iO 1 



^ 





t>i=4W 



Fig. 27. Induction CoiL {See text.) 



shock, which can be easily graduated by the use of the 

 well-known sliding induction coil (fig. 27), in which the 



