342 PROTOPLASMIC ACTION AND NERVOUS ACTION 



tinctly lower order (Qio = 1.5-2).' The significance of 

 this fact is not altogether clear, but it suggests that purely- 

 physical factors play more part in the destruction than 

 in the reconstruction of the surface-film. There are 

 general reasons for expecting that a process of structural 

 breakdown, in which purely physical factors predominate, 

 will have a low temperature coefficient; accordingly, 

 since protoplasmic transmission is apparently dependent 

 on such a breakdown, it is not surprising that its 

 temperature-coefficient should be lower than that of the 

 recovery process, which presumably is chiefly a result 

 of metabolic reconstruction. Let us suppose that the 

 first stage in the local excitation-process consists in a 

 removal or destruction, by chemical reaction, of those 

 constituents of the plasma membrane which are respon- 

 sible for its semi-permeabflity and coherence; and that 

 the second stage, immediately following, is some purely 

 physical process of disintegration or falling apart, in 

 which diffusion-processes are the chief factor. Then the 

 chemical temperature-coefficient will be shown by the 

 first stage only, while the second and probably longer 

 stage wiU have the coefficient of diffusion-processes. 

 The whole process will then have a low temperature- 

 coefficient similar to that observed, as the following 

 simple calculation shows. 



We assume that the total period of breakdown at 

 20° has a duration of 3 o- (about the duration of the rising 



' For the temperature coeflQcient of the nerve impulse cf. Maxwell, 

 Journal of Biological Chemistry, III (1907), 359; Snyder, American 

 Journal of Physiology, XXII (1908), 179; Harvey, Carnegie Institute 

 Publications, CXXXII (1910), 35; Lucas, Journal of Physiology, 

 XXXVII (1908), 112. For the transmission of the contraction wave 

 muscle cf. Woolley, Journal of Physiology, XXXVII (1908), 122; 

 Lucas, ibid., XXXIX (1909), 207. 



