116 THE PHYSIOLOGY OF MUSCLE AND NERVE. 



same range of temperature lies around 1 or between 1 and 

 2. Snyder* finds, on comparing the velocities of the impulse 

 at different temperatures, that they follow van't Hoffs law for 

 chemical reactions, that is, the velocity is approximately doubled 

 by a rise of 10 C. in temperature within physiological limits, 



velocity at T n + 10 mi . 



or, expressed in more general terms, -. : L. = 2. This 



' velocity at Tn 



effect of temperature on the velocity of the impulse is shown 

 graphically in Fig. 53. Anesthetics and narcotics,! such as ether, 



Fig. 53. Figure to show the effect of temperature on the velocity of the nerve impulse. 

 At each temperature two contractions of the gastrocnemius were recorded, one when the 

 nerve was stimulated close to tne muscle, one when it was stimulated further away (44 mm.). 

 The horizontal distance between the curves as they rise can be expressed in time by refer- 

 ence to the tuning-fork vibrations (200 per second) given below. For intervals of 10 C. 

 it will be seen that the velocity, as indicated by the reciprocals of the distances between 

 the pairs of curves, indicates a coefficient of two. (Snyder.) 



chloroform, cocain, chloral, phenol, alcohol, etc., may be applied 

 locally to a nerve trunk, and if the application is made with care 

 the conductivity and irritability may be lessened or suspended 

 entirely at that point, to be restored again when the narcotic 

 is removed. It is an interesting fact that the conductivity of 

 the nerve may be suspended also by deprivation of oxygen,J 

 that is, by local suffocation or asphyxia. A nerve fiber sur- 

 rounded by an oxygen-free atmosphere will slowly lose its 

 conductivity, and this property will be restored promptly upon 

 the admission of oxygen. Compression of a nerve will also 

 suspend its conductivity without permanently injuring the 

 fibers, provided the pressure is properly graduated. Lastly, 

 as was explained in a preceding chapter, the conductivity of the 

 nerve may be increased or decreased or suspended entirely by the 

 action of a galvanic (polarizing) current. This method of sus- 

 pending conductivity temporarily has been frequently employed 



* Snyder, " American Journal of Physiology," 22, 179, 1908. 

 t Frohlich, "Zeitschrift f. allgemeine Physiol.," 3, 75, 1903. 

 t Baeyers, ibid., 2, 169, 1903. 



