INCIPIENT AND ACTUAL CONTRACTION 67 



When the intensity of stimulus was raised to 3 units there 

 was an actual contraction. 



Fig. 30. Effect of continuous electric stimulation. Intensities 

 of stimuli, 0-5, I, and 3 units; corresponding records from 

 left to right. 



Note actual shortening of the organ under 3 units (Crinum). 



Continuity between Incipient and Actual 



Contraction 



It will thus be seen that external stimulation induces 

 a reaction which is of opposite sign to that of normal grow^th- 

 elongation. This retardation may be conveniently described 

 as ' incipient ' contraction ; for under increasing intensity of 

 stimulus the contractile reaction opposing growth-elonga- 

 tion becomes more and more pronounced ; at an inter- 

 mediate stage this results in an arrest of growth ; at a 

 further stage it culminates in an actual shortening of the 

 organ. There is no break of continuity between these stages. 

 I shall, therefore, use the term ' contraction ' in a wider 

 sense, including the ' incipient ' stage which finds expression 

 in retardation of growth. 



In Table VIII are given the results of typical experi- 

 ments on the effect of stimulation of increasing intensity 

 and duration. 



