94 



LECTURES AND ESS A YS 



VITALITY 



[1863] 



THE origin, growth, and energies of 

 living things are subjects which have 

 always engaged the attention of thinking 

 men. To account for them it was usual 

 to assume a special agent, free to a great 

 extent from the limitations observed 

 among the powers of inorganic nature. 

 This agent was called vital force ; and, 

 under its influence, plants and animals 

 were supposed to collect their materials 

 and to assume determinate forms. Within 

 the last few years, however, our ideas of 

 vital processes have undergone profound 

 modifications ; and the interest, and 

 even disquietude, which the change has 

 excited are amply evidenced by the dis- 

 cussions and protests which are now 

 common regarding the phenomena of 

 vitality. In tracing these phenomena 

 through all their modifications, the most 

 advanced philosophers of the present 

 day declare that they ultimately arrive 

 at a single source of power, from which 

 all vital energy is derived ; and the dis- 

 quieting circumstance is that this source 

 is not the direct fiat of a supernatural 

 agent, but a reservoir of what, if we do 

 not accept the creed of Zoroaster, must 

 be regarded as inorganic force. In short, 

 it is considered as proved that all the 

 energy which we derive from plants and 

 animals is drawn from the sun. 



A few years ago, when the sun was 

 affirmed to be the source of life, nine 

 out of ten of those who are alarmed by 

 the form which this assertion has latterly 

 assumed would have assented, in a general 

 way, to its correctness. Their assent, 

 however, was more poetic than scientific, 

 and they were by no means prepared to 

 see a rigid mechanical signification 

 attached to their words. This, however, 

 is the peculiarity of modern conclusions : 

 that there is no creative energy whatever 

 in the vegetable or animal organism, but 

 that all the power which we obtain from 

 the muscles of man and animals, as much 



as that which we develop by the combus- 

 tion of wood or coal, has been produced 

 at the sun's expense. The sun is so much 

 the colder that we may have our fires; he 

 is also so much the colder that we may 

 have our horse-racing and Alpine climb- 

 ing. It is, for example, certain that the 

 sun has been chilled to an extent capable 

 of being accurately expressed in num- 

 bers, in order to furnish the power which 

 lifted this year a certain number of 

 tourists from the vale of Chamouni to 

 the summit of Mont Blanc. 



To most minds, however, the energy 

 of light and heat presents itself as a 

 thing totally distinct from ordinary 

 mechanical energy. Either of them can 

 nevertheless be derived from the other. 

 Wood can be raised by friction to the 

 temperature of ignition; while by properly 

 striking a piece of iron a skilful black- 

 smith can cause it to glow. Thus, by 

 the rude agency of his hammer, he gene- 

 rates light and heat. This action, if 

 carried far enough, would produce the 

 light and heat of the sun. In fact, the 

 sun's light and heat have actually been 

 referred to the fall of meteoric matter 

 upon his surface ; and, whether the sun 

 is thus supported or not, it is perfectly 

 certain that he might be thus supported. 

 Whether, moreover, the whilom molten 

 condition of our planet was, as supposed 

 by eminent men, due to the collision of 

 cosmic masses or not, it is perfectly 

 certain that the molten condition might 

 be thus brought about. If, then, solar 

 light and heat can be produced by the 

 impact of dead matter, and if from the 

 light and heat thus produced we can 

 derive the energies which we have been 

 accustomed to call vital, it indubitably 

 follows that vital energy may have a 

 proximately mechanical origin. 



In what sense, then, is the sun to be 

 regarded as the origin of the energy de- 

 rivable from plants and animals? Let 



