OF VITAL FORCE, AND THE CONDITIONS OF ITS EXERCISE. 



143 



ence of the same forces, that our notion of their properties entirely rests ; and 

 to say that all matter which is capable of becoming organized possesses "vital 

 properties/' is merely to affirm, in other words, that it is capable of being made 

 a part of a living structure, and of -becoming the instrument of operating after 

 the same fashion upon other matter leaving the question as to the source or 

 origin of the force which thus changes it, or by which it induces changes in other 

 matter, just where it was. 



123. The doctrines which have been just now glanced at, as expressing the 

 present aspect of Physical Science, whilst they indicate the fallacy of some of 

 what have been considered the established principles of Physiology, conduct us 

 at the same time to a new and more satisfactory solution of the problem. Look- 

 ing at the phenomena of Life from the same point of view as that from which 

 we are now taught to regard those of Physical Science namely, as the results 

 or manifestations of a certain kind of force, acting through those forms of matter 

 which we term organized we are further led to seek for its source, not in the 

 organism itself, but in some power external to it. And this power we find in 

 those Physical agencies, Light, Heat, and Electricity, which have been com- 

 monly accounted "Vital Stimuli/' their operation, either singly or in combina- 

 tion, having long been recognized as necessary to enable an organized structure 

 to manifest vital phenomena. Thus, Light, acting upon the living Vegetable 

 cell, makes it the instrument of decomposing carbonic acid, water, and ammonia, 

 and of generating organic compounds which the Chemist has not yet been able 

 to imitate ; and the amount of carbonic acid thus decomposed has been found to 

 bear a constant ratio (cseteris paribus) to the illuminating power of the rays 

 which it receives. 1 The agency of light, however, is chiefly exerted in prepar- 

 ing the pabulum to be appropriated by the organism ; and we see, in the germi- 

 nating seed, that where this has been previously ela-borated, light is not required 

 for its conversion into living tissue. But for this purpose, a certain measure of 

 Heat is required; and the rate of germination, that is, the rate at which the 

 organizable material is converted into living tissue, is determined (within certain 

 limits) by the degree in which that agent is in operation. In the Animal king- 

 dom, for which, as for the germinating seed, the nutrient material is already 

 provided by a pre-existing vegetation, the dynamical influence of Light is of 

 comparatively little importance; but we have abundant evidence, in the life of 

 the "cold-blooded" tribes, which are destitute of the power of maintaining an 

 independent temperature, that the rate of vital activity, as manifested both in 

 the phenomena of growth and development, and in the production of nervo- 

 muscular force, is determined (within certain limits) by the amount of Heat 

 to which the individual is subjected. This dependence is no less real and 

 immediate in the case of warm-blooded animals ; but it is rendered less apparent 

 by the uniformity of temperature which they are enabled to sustain. Of the 

 degree in which the ordinary phenomena of Life are dependent upon Electricity 

 acting upon the organism from without, we as yet know next to nothing ; the 

 mode in which they are affected by this agent not having been yet precisely 

 determined. It can scarcely be doubted, however, from what is known, that it 

 stands in very close relation to Vital force, and is capable of exerting an ex- 

 tremely powerful influence upon its operations. 



124. It seems, then, to be a legitimate expression of the dynamical conditions 

 requisite for the production of the phenomena which we distinguish as Vital, to 

 say that they are dependent, directly or indirectly, upon the Physical forces 

 pervading the Universe; which, acting through organized structure as their 

 " material substratum/' manifest themselves as Vital Force, one of the most 

 characteristic operations of this being the production of new tissue, which in its 



1 See Prof. Draper " on the Forces which produce the Organization of Plants," p. 177. 



