THE VITAL AND PHYSICAL FORCES. 
729 
of its operation ; following the same mode of inquiry for this purpose, as that which 
has been found successful in other departments of scientific investigation. In doing 
this, it has been necessary for them to isolate, as much as possible, those phenomena 
which may be regarded as Chemical or Physical, from those which must be distin- 
guished as Vital ; in order that, by the collocation and comparison of the latter, their 
mutual relations may be discovered. Still, after making every possible allowance 
for the operation of chemical and physical agencies, in the direct production of the 
changes of composition, mechanical movements, &c. which connect living beings 
(so to speak) with the universe around them, it is impossible for the discriminating 
inquirer not to see, that the influence of these agencies is indirectly exerted, to a yet 
greater extent, in the production or modification of purely vital phenomena. Thus, 
to take a very simple case, it cannot be for a moment doubted that heat and light 
exert an influence upon the vegetable germ, which is essential to its growth and de- 
velopment into the perfect plant, and to the performance of all the actions of the 
latter, whether these have reference to the extension of its own fabric, to the forma- 
tion of organic compounds from the materials supplied by the inorganic world, or to 
the production of the germs of new individuals which are in like manner to go through 
the same series of phases. Hence light and heat have been designated as vital 
stimuli ; ” the current idea being, that their agency upon the vegetable germ excites or 
awakens the forces which were dormant in it ; and that, by enabling it thus to as- 
similate the new materials supplied by the inorganic world, and to give to these the 
structure of organized bodies, they contribute to develope the latent powers of these 
materials, which in their turn exhibit vital properties as they are made to form part 
of organized structures. Such, at least, is the doctrine of those who have most 
clearly expressed themselves upon the relation of the “vital stimuli” to the “vital 
properties ” of organized bodies ; and the author has not been able to find in phy- 
siological writings, any indication of a more intimate relationship between the physical 
forces and vital phenomena, than that just stated, — save on the part of those who 
have vaguely identified Heat or Electricity with the “ vital principle,” with about 
the same amount of philosophical discrimination as that which was exercised by 
the iatro-chemists and iatro-mathematicians of the sixteenth and seventeenth cen- 
turies. 
The views of physical philosophers have been directed of late almost exclusively to 
the dynamical aspect of the inorganic universe ; that is to say, its phenomena have 
been studied as the manifestations of certain forces ; and each department of science 
takes cognizance of one or more of these, its general laws being nothing else than 
expressions of the modes and conditions of their operation, so far as known to the 
scientific investigator. That among all these forces there are very intimate mutual 
relations, is a conviction which has been gradually increasing in strength in the minds 
of philosophical inquirers during the whole of the present century ; in consequence of 
the extraordinary development which the sciences of Chemistry, Electricity, Mag- 
MDCCCL. 5 A 
