26 OF LIFE, AND ITS CONDITIONS. 



mutually-related changes which ma} 7 be designated the Life of the Universe, 

 the Physicist has been led in the first instance to recognize several distinct 

 modes of activity, e.g., Mechanical and Chemical, Electrical and Thermal ; 

 and then, prosecuting his analysis under the guidance of that idea of Power 

 which he finds in his own sense of effort, has been brought to refer every 

 effect to a causative Force of some kind, acting through a certain Material 

 instrumentality : so the Physiologist who makes the living organism his 

 study, is led in the first place to refer its peculiar phenomena to a set of 

 categories as distinct from the preceding as they are from each other; and 

 thence to distinguish between their instrumental and their dynamical condi- 

 tions, the Organic Structure and the Vital Forces which animate it. But 

 furtluT, as the Physicist, in proportion to the elevation of his standpoint 

 and the comprehensiveness of the survey he can thence take of the phe- 

 nomena of the Inorganic Universe, is enabled to discern, first the mutual 

 relation, and at last the essential unity, of all those Forces whose manifes- 

 tations appeared so diverse when separately contrasted : so may the Physi- 

 ologist, in proportion to the insight he gains into the peculiar characteristics 

 of Vital Activity, come in the first instance to recognize the mutual rela- 

 tion of the agencies which underlie its diversified phenomena, next to per- 

 ceive their fundamental unity as so many expressions of one and the same 

 Vital Force acting through different material instrumentalities, and finally 

 to discern the essential identity of this force with that which maintains the 

 ceaseless cycle of activity in the Universe at largo. 1 



3. If, now, we inquire what it is that essentially distinguishes Vital from 

 every kind of Physical Activity, we find this distinction most characteris- 

 tically expressed in the fact, that a germ endowed with Life develops itself 

 into an Organism of a type resembling that of its parent; that this organ- 

 ism is the subject of incessant changes, which all tend in the first place to 

 the evolution of its typical form, and subsequently to its maintenance in 

 that form, notwithstanding the antagonism of Chemical and Physical agen- 

 cies which are continually tending to produce its disintegration ; but that, 

 as its term of existence is prolonged, its conservative power declines, so as 

 to become less and less able to resist these disintegrating forces, to which it 

 finally succumbs, leaving the organism to be resolved by their agency into 

 the components from which its materials were originally drawn. The his- 

 tory of a Living Organism, then, is one of incessant change;'* and the con- 

 ditions of this change are to be found partly in the organism itself, and 

 partly in the external agencies to which it is subjected. 



4. But the Life of any complex organism, such as that of Man, is the 

 aggregate of the Vital Activity of all its component parts ; and we must 



1 See the Author's Memoir, On the Mutual Relations of the Vital and Physical 

 Forces, in the Philosophical Transactions for 1850 



2 If change be essential to our idea of Life, it may be asked what is the condition 

 of a Seed, which may remain unaltered during a period of many centuries, vegetat- 

 ing at hir-t, when placed in favorable circumstances, as if it had only ripened the 

 year before. We can .-carcely call it alive, for it is not performing any vital oper- 

 ation. Hut it is not dead; tor it has undergone no disintegration, and retains its 

 capacity fur Hrhir/, whi'-h is analogous to the potential energy of the Physicist. The 

 most correct designation of such a state (which can only be maintained under a com- 

 plete seclusion Irom disintegrating agencies) seems to be </<>/-/<n/t vitality. Certain 

 Animals may be reduced to it: as the Frog by cold, mid the Wheel-animalcule by 

 slow desiccation Organisn capable of undergoing such a suspension of activity 

 may be kept in a dormant condition so long as disintegrating agencies are excluded ; 

 but the very conditions (as heat in the. one case, moisture in the other, and both 

 combined in th'- ca>c of the seed) whose proence is followed by the renewal of active 

 life it' the organ i.-m has undergone no injurious change, insure its speedy decaj if it 

 be not able to resume its proper vital activity. 



