36 INTRODUCTION. 



but out of these we single warmth as the dynamical condition; whilst the 

 oxygen and the water, with the organized structure of the seed itself, and the 

 organic compounds which are stored up in its substance, constitute the material. 

 A strictly scientific inquiry, then, must recognize Dynamical agency, as well 

 as Material condition ; and it will be found that this is peculiarly requisite in 

 the Science of Life, which has been pursued by some as if it were a sufficient 

 account of every phenomenon not otherwise explicable, to refer it to a " vital 

 principle;" whilst others have endeavored to reduce all Physiological causation 

 to a set of material conditions, maintaining that Life entirely depends on " organi- 

 zation/' and that the hypothesis of a vital principle is consequently unnecessary 

 and unphilosophical. Others, again, who have recognized the operation of Phy- 

 sical and Chemical agencies in the living body, have maintained that all Vital 

 action is but a peculiar manifestation of heat, mechanical power, chemical affinity, 

 and the like ; and have thus attempted to break down the barrier between the 

 Organized and the Inorganic creation. The Author has elsewhere 1 endeavored 

 to show, that we have evidence of the operation of a power in the living body, 

 whose manifestations are so different from those of any of the Physical Forces, 

 that we cannot reasonably refrain from giving it a distinctive designation ; and 

 that this " Vital Power" may exert itself in a great variety of modes, and may 

 consequently produce a great variety of phenomena, according to the material 

 conditions of its operation, just as (though the comparison be somewhat clumsy) 

 the mechanical power which turns the engine-shaft in an extensive factory, is 

 rendered efficient for an immense variety of purposes, according to the construc- 

 tion and arrangement of the several machines through which it is distributed. 

 And further, he has attempted to prove, that the source of this Vital Power is 

 to be found, not in the organization of the being itself, but in the forces which 

 operate upon it ab externo; and that it has the same close and intimate relation 

 with the Heat, Electricity, Chemical Affinity, and other agencies of the In- 

 organic world, which they have been proved to have with each other : so that, 



just as Heat acting upon water generates Mechanical force, or when applied to 



\ 

 a certain combination of metals excites Electricity, so, when brought to bear 



upon a torpid animal or upon a seed (in which the material conditions of this 

 activity are present), it manifests itself as Vital Force, and is the immediate 

 dynamical condition of the phenomena of growth, development, &c. 



But further, the term Cause has a Theological as well as a Scientific sense; and, 

 like the two usages of the term Law, these two acceptations are perfectly har- 



1 See his Memoir "On the Mutual Relations of the Vital and Physical Forces," in the 

 Philosophical Transactions for 1850. 



