230 PHYSIOLOGY CHAP. 



a certain point, suddenly disappears. Kecovery takes place in the 

 same way ; excitability gradually rises, while conductivity suddenly 

 returns in its former proportions as soon as the excitability has 

 risen to its normal level (Fig. 145). 



Von Baeyer (1902), in Verworn's laboratory, carried out 

 another series of researches on the effect of oxygen and the in- 

 different gases (nitrogen and hydrogen) upon the vitality of nerve. 

 By means of Griinhagen's method, which he improved in certain 

 details (Figs. 146 and 147), he established the following results, 

 which are complementary to those of his predecessors : 



FIG. 145. Diagram to show changes of excitability and conductivity in a motor nerve under the 

 influence of anaesthetising and asphyxiating agents upon a limited portion. (Fr. W. Frohlich.) 

 The abscissa line shows the time in minutes ; the ordinates, the distance in mm. of the coils at 

 which the minimal stimulus (single induction shock) takes effect. 



(a) Under the direct asphyxiating influence of the indifferent 



ises, the excitability of nerve disappears in three to five hours, 

 n substituting oxygen for these gases, normal excitability returns 

 after three to ten minutes. 



(&) The physiological conductivity of the nerve is also abolished 

 by the asphyxiating gases, and recovered on adding oxygen. 



(c) Asphyxia loss of excitability and conductivity spreads 

 along the nerve in a centrifugal direction according to the Kitter- 

 Valli law (infra); functional recovery when oxygen is supplied 

 seems, on the contrary, to be propagated in a centripetal direction. 



(d) On raising the temperature of the nerve to 42-47 C. the 

 indifferent gases produce asphyxia in twenty to sixty minutes. If 

 the temperature be then lowered again to that of the surrounding 



