io8 RESPONSE IN THE LINING AND NON-LIVING 



the response-curves. The form of these curves, sti- 

 mulus remaining constant, will be modified by friction ; 

 the less the friction, the greater is the mobility. The 

 friction may be varied by more or less raising a vessel 

 of sand touching the pendulum. By varying the 

 friction the following curves were obtained. 



(a) When there is little friction we get an after- 

 oscillation, to which we have the corresponding pheno- 

 menon in the retinal after-oscillation (compare fig. 105). 



(b and c] If the friction is increased, there is a 

 damping of oscillation. In (c) we get recovery-curves 

 similar to those found in nerve, muscle, plant, and 

 metal. 



(d) If the friction is still further increased the maxi- 

 mum is reached much later, as will be seen in the 

 increasing slant of the rising part of the curve ; the 

 height of response is diminished and the period of 

 recovery very much prolonged by partial molecular 

 arrest. The curve (d) is very similar to the ' molecular 

 arrest ' curve obtained by small dose of chemical reagents 

 which act as ' poison ' on living tissue or on metals 

 (compare fig. 93, a). 



(e) When the molecular mobility is further decreased 

 there is no recovery (compare fig. 93, b). 



Still further increase of friction completely arrests 

 the molecular pendulum, and there is no response. 



From what has been said, it will be seen that if in 

 any way the friction is diminished or mobility increased 

 the response will be enhanced. This is well exemplified 

 in the heightened response after annealing (fig. 58) and 

 after preliminary vibration (figs. 81, 82). 



