iv GENEKAL PHYSIOLOGY OF NERVOUS SYSTEM 207 



the nerve produces carbonic acid during its activity ; but there is 

 so far no direct demonstration of this fact. It has, indeed, as we 

 shall see, been demonstrated of late years by the school of Verworn 

 (H. v. Baeyer, Fr. W. Frohlich) that the nerve requires a supply 

 of oxygen to keep up its vitality. Thunberg succeeded in 

 measuring the quantity of oxygen absorbed and of carbonic acid 

 given off. But no one has yet proved that this respiratory gas 

 exchange depends directly upon the state of rest or activity of 

 the nerve. Funke found that the normally alkaline reaction was 

 converted into an acid reaction in a nerve treated with strychnine, 

 owing to its exaggerated activity, but this observation has not 

 been confirmed by other workers. Kohmann, who experimented 

 on the nerves of the electrical organ of Torpedo, using acid fuchsin 

 as his reagent, failed to obtain any positive result. 



The exceedingly slow character of nerve metabolism can also 

 be detected in the fact that, unlike the grey matter, which is 

 irrigated by a rich network of blood capillaries, the vascularisa- 

 tion of nerve is very little developed. But the best argument, of 

 which we shall give experimental proof later on, is the fact that 

 nerve, unlike the nerve-centres, is practically inexhaustible, i.e. it 

 shows no visible signs of fatigue, even when thrown into a state 

 of activity for several hours. 



Thermal phenomena, again, such as are due to katabolic 

 processes, are very small and insignificant in the active nerve. 

 Schiff found a slight increase in heat development when he 

 applied the thermo-electric pile to nerve. But the same method 

 yielded negative results in the hands of other expert observers 

 (Helmholtz, Heidenhain). Nor did Eolleston arrive at any 

 positive result with Callender's extremely sensitive method. 



It seems impossible to doubt that metabolism is very low in 

 nerve-fibre, even after strong and persistent stimulation, which 

 evidently means that the work the nerve has to perform is 

 inconsiderable. Both when the excitation is propagated from the 

 periphery to the centre (afferent nerves) and when it travels from 

 the centre to the periphery (efferent nerves), the nerve only needs 

 to send a slight impulse, a tiny spark, to the end - organ with 

 which it is connected in order to effect a vigorous process and 

 marked explosion of energy, owing to the great irritability of 

 that organ. 



Yet, however slight it may be, the process of excitation and 

 conduction in the nerve-fibre must involve a certain consumption 

 of energy. That the products of chemical dissociation and the 

 correlative development of heat are not demonstrable even after 

 strong and protracted stimulation, suggests that the chemical 

 dissociation is rapidly compensated by a process of restitution. 

 Gad, in formulating this notion more precisely, assumes that the 

 restitution of the substance that has been altered by excitation 



