292 NERVOUS FORCE. L.ECT. XIV. XV. 



either by means of heat, or by electricity developed by it. 

 In other words, it is possible to ascertain whether we ob- 

 tain with steam-engines, or electro-magnetic apparatus, 

 and by means of a determined chemical action, a mecha- 

 nical effect equal to, or different from, that which is pro- 

 duced when this same action takes, place within an animal* 



But before commencing this investigation, I cannot re- 

 frain from observing,, that, in order to establish this com- 

 parison, it is necessary to assume one of the two following 

 hypothesis : we now know that heat, electricity, and ner- 

 vous force, are developed in animals^ and we assume that 

 the causes of their production reside in the ehemical ac- 

 tions of nutrition. But we may suppose that they are pro- 

 duced in certaia constant quantities, and independently 

 one of the- othe^; or, indeed, that from a certain chemi- 

 cal action there never follows but a certain quantity of force, 

 whatever be the form in which it is manifested. 



In order to. make myself better u-nderstood, I will give 

 an example : zinc burrns in oxygen, producing light and 

 heat ; this same zinc can be oxydized by decomposing 

 water and developing only heat, o* heat and electricity, if 

 we touch it with platinum wire. Suppose, now, that we 

 could transform these forces into a certain quantity of me- 

 chanical work done by them, we might say that the sum of 

 these quantities is the same in every case, and that when 

 one happens to fail, the other is substituted for it, by a 

 relative quantity drawn froi- their mechanical equivalents. 

 But it might equally happen, that they were developed in- 

 dependently of each other. Experiment would reply in 

 favour of this latter opinion. I measured the heat disen- 

 gaged by zinc oxydized by decomposing water, and I re- 

 peated this experiment by having, in addition, the disen- 

 gagement of the electric current ; the beat was invariably 



