LECT. XIV. XV. PRODUCTION OF NERVOUS FORCE. 293 



the same, and nearly equal to that which zinc produces 

 when oxydizing by burning in oxygen. 



We might then consider all the chemical action of car- 

 bon which combines with oxygen in animals, as the cause 

 of nervous force, independently of the heat and electricity 

 that it may produce ; and we would ask whether this ac- 

 tion, taking place in the animal itself, determines an effect 

 analogous to, or different from, that which it would deter- 

 mine, if it occurred in a steam-engine or in an electro-mag- 

 netic apparatus. 



While travelling on one occasion with the celebrated 

 Robert Stephenson, we were obliged to send a man on foot 

 forty miles. I asked Mr. Stephenson what quantity of car- 

 bon was necessary to transport a man forty miles by a loco- 

 motive. He replied, about 5 kilogrammes [about 11 Ibs. 

 avoirdupoise.] 



The person we had despatched accomplished his journey, 

 by walking, in less than ten hours, consuming by his respi- 

 ration a quantity of carbon not exceeding 150 grammes, 

 that is about ^ of the quantity which would have been ne- 

 cessary if this transit had been effected by a locomotive. 

 M. Dumas has calculated how much carbon would be 

 burnt in a steam-engine, in conveying a man from the level 

 of the sea to the summit of Mount Blanc. The quantity 

 would be from 1000 to 1200 grammes ; but a man ac- 

 complishes this feat by a two days' march, and consumes 

 only 300 grammes. The difference in the second example 

 is not so great as in the first ; because the useful result 

 which we obtain from a stationary steam-engine, is much 

 more considerable than that from a locomotive. It is 

 equally true that the difference is very great, and that the 

 work produced from nervous force derived from a certain 

 chemical action, is much greater than that which this same 

 action produces when converted into heat. 



