108 RESPONSE IN THE LIVING 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). 
(6 andc) If the friction is increased, there is a 
damping of oscillation. In (ce) we get recovery-curves 
similar to those found in nerve, muscle, plant, and 
metal. 
(7) 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, 0). 
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 willbe enhanced. This is well exemplified 
in the heightened response after annealing (fig. 58) and 
after preliminary vibration (figs. 81, 82). 
