BRINK AND OTHERS: CHEMICAL EXCITATION OF NERVE 467 



An increased rate of oxidation is essential for the initiation of im- 

 pulses. That is shown by the effects of an oxidation-inhibiting agent, 

 such as sodium azide. A portion of a nerve trunk was placed in sodium 

 citrate, and impulses which were thus developed were recorded in one 

 of the fibers coming from the chemically activated region. Sodium 

 azide was then applied to the citrate-treated portion of the nerve, in 

 a concentration that was sufficient to suppress the chemical excitation. 

 For this, a concentration of azide which restored the oxidation to a 

 normal rate was adequate (figure 10). After the rhythmic discharge 



300 



200 



a. 



100 - 



AZIDE 



2 3 



MILLIMOLES PER LITER 



Figure 10. The respiration of a calcium-deficient nei-ve (per cent of value in reference solu- 

 tion) suppressed by sodium azide, as is the respiration of a normal nerve. 



of impulses had thus been inhibited, it was still possible, for several 

 hours to send a high frequency train of impulses, initiated by electric 

 stimuli, through the calcium-deficient and azide-treated length of nerve. 

 The initiation of impulses by a calcium-deficient region of nerve re- 

 quires a higher rate of oxidation than is necessary for the maintenance 

 of the capacity of such a calcium-deficient region to conduct impulses. 

 Certain specific chemical changes in the constitution of nerve and in- 

 creased metabolic rate both appear to be necessary for the initiation of 

 rhythmic activity. One without the other is an inadequate condition 

 for self-excitation. 



