NATURAL HISTORY OF ORGANIZED BODIES. 287 



cliemistry : it has extended the domain of chemical analysis beyond the world 

 we inhabit, by enabling us, from the optical properties of the light of the stars, 

 to determine their chemical composition, ancl to atlirm, for example, that in the 

 sun there must be iron, nitrog'en, cobalt, &c. ; in the star Aldebaran, sodium, 

 magnesium, calcium, iron, mercury, hydrogen, &c. Thus science, by means of 

 analysis, has realized wonders which the most daring imagination would have 

 never ventured to conceive. 



In i)hysios, the functions of analysis are not less extensive. It is by employ- 

 ing dili'erent kinds of apparatus, each of which reveals certain properties of elec- 

 tricity, liglitj heat, &c., that we have succeeded in forming an idea of the man- 

 ner in which tliese agents act in nature. The physicist renounces the idea of 

 ascertaining their essence as we renounce a knowledge of the essence of life, 

 and is content to describe each agent according to its manifestations. Eh,'ctri- 

 city, which reveals itself to us in great meteorological effects, in the production 

 of lightning and boreal auroras, for instance, everywhere else evades our per- 

 ception, and yet it is demonstrable that everywhere in nature electricity exists. 

 The electroscope discloses it in the atmosphere which suiTounds us. The gnlmn- 

 ometcr shows us that electric cun-ents are formed, so to say, wherever an act of 

 a physical nature is accomplished : water which evaporates, a plant which vege- 

 tates, an animal which lives, give rise to electric phenomena which our senses 

 cannot directly perceive, but which we render perceptible by means of instru- 

 ments of analysis. Such expressions as electric currents^ electro-mot ice forces, 

 ■intensity and tension of clectricit}^, are artifices of language which enable us to 

 conceive more readily the conditions under which the phenomena called elec- 

 trical are produced and modified. But in proportion as known facts become 

 multiplied by analytic researches, science is seen to disengage itself from the 

 ambiguities of language and to sacrifice the expressions whiclk are no longer 

 useful to it. It is thus that the hypothesis of two electric fluids, the one 2)ositive, 

 the other negative, is tending at present to disappear. 



What we know regarding light has been acquired by the same method : we 

 have learned to decompose it by the jjm>/Y into its different elements ; some col- 

 ored in difierent manners, others invisible, but endued with heat or chemical 

 properties. The theory of light furnishes us with a good example of the dis- 

 appearance of an hypothesis in the presence of contradictory facts. We know 

 that the hj-jDothesis of radiation has vanished before the phenomenon of inter- 

 ferences, and has given place to the theory of undulations, which alone explains 

 all the phenomena actually known. 



Thus physical agents become characterized every day in a more complete 

 manner, and are more and more accurately determined by the cliaracters which 

 their analysis discloses. I shall not attempt to follow the progress realized by 

 the analytic method in the knowledge of magnetism, heat, mechanical force, &c. 

 I confine myself to the statement already made that the solidarity of the 

 sciences constantly augments in proportion to the progress realized. For the 

 difierent branches of physics the fusion is evidently taking place in our own day. 

 It is interpreted to us by the profound conception of the equivcdence of forces 

 and of the transformation of mechanical labor into heat or into electricity. 



The naturalist who is not content with obscn'ing the forms, however varied, 

 of organization in animals and plants, must proceed like the physicist and chem- 

 ist, if he desires to discover the conditions of life. His first means for the 

 analysis of phenomena is vivisection. It is through this that he becomes a w"it- 

 ness of the accomplishment of functions; all that is visible and palpable in the 

 play of the organs Ife revealed to him by tlias anatoniia animatu, as it was called 

 by Ilaller. On this head I could say nothing which will not be found more 

 competently stated in the valuable treatise of M. CI. Bernard (Introduction a la 

 Medicine experimcntcde.J In this work may be seen everything relative to phy- 



