LATENT PERIOD AND REFRACTORY PERIOD 273 



Refractory period. — We shall next consider the pecu- 

 liarities of the refractory period which I have discovered in 

 the case of plant-tissues ; and for the material of this investi- 

 gation we shall use the plant Biophytum, taking, in fact, the 

 very specimen whose successive responses have already dis- 

 played such remarkable consistency (fig. 112). Such uni- 

 formity in successive responses is only possible when we 

 allow sufficient time of rest for complete protoplasmic re- 

 covery, by which the excitability is fully restored. But it has 

 been shown in Chapter XX. that if sufficient time of rest be 

 not allowed, the protoplasmic recovery is incomplete, and the 

 excitability is diminished. Hence the extent of response, 

 which is an outward indication of excitability, is diminished, 

 and this effect is known as fatigue. 



We also arrived, in the same chapter, at the theoretical 

 conclusion that there is a minimum resting interval, the dimi- 

 nution of which results in such a loss of excitability as to 

 abolish response, and this period we know as the Refractory 

 Period, because the leaf then apparently takes no account of 

 stimulus, or is 'refractory' to it (fig. 105J. We shall now 

 enter into greater detail regarding the peculiarities of this 

 refractory period. After taking the six curves in response to 

 separate single stimuli which were so extraordinarily similar, 

 I proceeded to take a curve of response to two equal stimuli 

 of the same intensity as before — namely, nine volts, charging 

 •01 microfarad — the two stimuli following each other at an 

 interval of one second. The application of the second stimu- 

 lus appeared to produce no effect, the extent and general 

 character of response being the same as in the case of single 

 stimulus, with only the difference of a slight elongation of the 

 flattened top of the curve. I next tried the effect of two 

 stimuli at an interval of five seconds. The leaflet was still 

 refractory to the second stimulation, but when I applied it at 

 an interval of ten seconds, the second stimulus became effec- 

 tive. It will thus be seen that Biophytum has rather a long 

 refractory period, during which, as far as can be seen, it takes 

 no account of the impact of a new stimulus. This refractory 



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