CHAPTER XIV 



MEMBRANE CHANGES DURING STIMULATION 

 REFRACTORY PERIOD 



We have already given reasons for regarding the 

 bioelectric variations as a result of structural change, 

 controlled by metabolic change, in the protoplasmic 

 surface layers. From this point of view another 

 constant accompaniment of the stimulation-process, 

 the refractory period, receives a consistent theoretical 

 explanation. The presence of the intact surface-film 

 is necessary for stimulation; if the film is broken down 

 as a consequence of stimulation, it must be re-formed and 

 restored to its original state before a second complete 

 stimulation is possible. This deduction is in agreement 

 with our general experience of stimulation-processes. 

 It is a striking fact that in all irritable tissues stimulation 

 is immediately followed by a period of inscnsitivity and 

 subnormal irritability; this period of temporar)^ depres- 

 sion, which is extremely brief in rapidly responding 

 tissues, is the refractory period, and there is evidence 

 that it corresponds to the period during which the film 

 is undergoing breakdown and reconstruction. During 

 the refractory period the tissue loses at the same time 

 both its susceptibility to electric stimulation and its 

 ability to transmit states of excitation; in other words, 

 there is a temporary loss of both irritability and conduc- 

 tivity.^ 



» Cf. Lucas and Bramwell, Journal of Physiology, XLII (191 1), 405; 

 Adrian, ibid., L (19 16), 345. 



337 



