ANIMAL ELECTRICITY. LECTURE II. 53 



sponses to the left of the Hght bar gives the normal 

 of this particular nerve — the light bar shows when 

 expired air was blown in — and the next twenty or 

 thirty responses give token of the altered state of 

 the nerve during the next twenty or thirty minutes. 

 The expired air contained 3 per cent, of CO^ and was 

 blown throuo'h the nerve chamber for two minutes. 



By other experiments it was ascertained that the 

 alteration was neither due to altered temperature nor 

 to anything else in the expired air but CO^. It is 

 then evident that nerve is extraordinarily sensitive 

 to CO,, and this clear fact will form the point of 

 departure of our further study. 



REFERENCES. 



The general notion of " internal respiration," the functional 

 attribute of all protoplasm, as distinguished from " ex- 

 ternal respiration," the accessory means, alluded to on 

 p. 48, is developed by Claude Bernard, in his Leqons 

 siir les PJienoinenes de la Vie couiniiuis aiix aniniaux et 

 aux vegetaux, vol. ii., Paris, 1879. The notion of the 

 double aspect of functional changes in living matter, 

 expressed in the terms — analysis and synthesis, breaking- 

 down and building-up, dissimilation and assimilation, 



