i04 



ON THE PRINCIPLE OP LIFE, 



laboratory, and spirited with the most active of her energies. An ap- 

 proach towards this hypothesis is also of great antiquity ; for it constituted 

 one of the leading features of the Epicurean philosophy, and is curiously 

 developed by Lucretius in his poem on the Nature of Things. According 

 to him, it is a gas or aura, for which in his day there was no name, diffused 

 through every part of the hving fabric, swifter and more attenuate than 

 heat, air, or vapour, with all which it concurs in forming the soul or mind 

 as its chief elementary principle 



Far from all vision this profoundly lurks, 

 Through the whole system's utmost depth diffused, 

 And lives as soul of e'en the soul itself.* 



But it is to the astonishing discoveries of modern chemistry alone that 

 we are indebted for any fair application of any such fluid to account for 

 the phasnomena of life. 



Among the numerous gases which modern chemistry has detected, 

 there are three which are pre-eminently entitled to our attention, though 

 they seem to have been glanced at by the Epicureans : caloric, or the 

 matter of heat, chiefly characterized in our own day as a distinct substance, 

 by the labours of Dr. Black and Dr. Crawford : oxygene, or the vital part 

 of atmospheric air, first discovered by Priestley, and explained by Lavoisier : 

 and the fluid which is collected by the Voltaic trough, and which is 

 probably nothing more than the electric fluid under a peculiar form. 



Of these caloric, as a distinct entity, was detected first. It was found 

 to be a gas of most astonishing energy and activity, and, at the same time, 

 to be of the utmost consequence to the living substance ; to exist mani- 

 festly wherever life exists, and to disappear on its cessation. It was 

 hence conceived to be the principle of Hfe itself. 



But oxygene began now to start into notice, and the curious and indis- 

 pensable part it performs in the respiration, as well as in various other 

 functions of both animal and vegetable existence, to be minutely explored 

 and ascertained, and especially by the microscopic eye of M. Girtanner.t 

 The genius of Crawford fell prostrate before that of Lavoisier. Oxygenic 

 was now regarded as the principle of hfe, and heat as its mere attendant 

 or handmaid. 



About the year 1790, Professor Galvani, of Bologna, accidentally disco- 

 vered that the crural nerve of a frog, which had been cut up for his dinner, 

 contracted and became convulsed ^n the application of a knife wetted with 

 water ; and following^ up thi? imple fact, he soon discovered also, that a 

 similar kind of contraction or convulsion might be produced in the mus- 

 cles of other animals, when in hke manner prepared for the experiment, 

 not only during lif?» but for a considerable period after death ; and that in all 

 such cases a fluid of sojne sort or other was either given to the contracting 

 body or taken from it. And Professor Volta, about the same period, suc- 



\ 



* Nam penitus prorsum latet hjec natura, subestque ; 

 Nec magis hac infra quidquam est in corpore nostro ; 

 Atque anima est animse proporro totius ipsa. 



De Rer. Nat. iii. 274. 



T Memoires sur I'lrritabilite, consideree comme principe de vie dans la nature organisee. 

 Paris, 1790. . 



J It IS a singular fact, that this identical discovery was not only made, but completed m 

 all its bearings, and by the same means of a recent dissected frog, by Dr. Alexander Stuart, 

 physician to the queen, in 1732, though no advantage was taken of it. A minute account 

 of Pr. Stuart's experiments is given in the Phil, Trans, for 1732. 



