4d ANIMAL ELECTRICITY.- — LECTURE II. 



the woman crot the best of the arorument, but the 

 man was right, and gave evidence, I think, of 

 superior imaginative power. We breathe by lungs, 

 so do all our personal friends among animals ; but 

 fishes breathe by gills, plants breathe by leaves, 

 and protoplasm, devoid though it be of diverse parts 

 or organs, breathes by direct take and give between 

 itself and the atmosphere. And in an organism 

 where the living units are buried away from the 

 atmosphere, lungs or gills, heart vessels and blood 

 are the intermediate instruments of this take and 

 give between protoplasm and air. Protoplasm, then, 

 directly or indirectly, takes from the air oxygen, and 

 gives to the air carbon dioxide, and such respira- 

 tion is the primitive essential function to which the 

 instrumental means — organs of respiration, organs 

 of circulation — are secondary and accessory compli- 

 cations. 



It has been said that "respiration is a slow com- 

 bustion," and Black, a century and a half ago, fifty 

 years before the discovery of oxygen by Priestley, and 

 the closer identification by the Lavoisier school of 

 respiration with combustion, showed that the end- 

 product of respiration is identical with that of com- 

 bustion. And even to-day, if we bear in mind that 

 the carbon dioxide produced by respiration (as indeed 

 that produced by combustion) is not a product of 

 direct 6xidation — that carbon and oxygen do not, so to 

 speak, meet and join hands directly, either in the lungs, 



