DR. PHILIP ON THE POWERS OF LIFE. 
375 
leading power in the sensitive system, being employed in many of the functions of the 
latter; by the sensorial being employed in one of the most important of the vital 
functions, this peculiarity of respiration, for in no other of those functions is there any 
such cooperation, extensively influencing the phenomena both of health and disease ; 
by both systems depending for the maintenance of their organs on the same powers, 
and more or less directly on each other ; by the powers common to both systems, 
the muscular power and the powers of the living blood, being under the influence of 
the leading powers of both ; and by all affections of whatever part necessarily in- 
fluencing both its sensitive and vital nerves, and consequently the leading powers of 
both systems. 
AS the various parts of each system are formed into a whole by all parts of each 
influencing and being influenced by its leading principle, so all parts of the animal 
body are formed into a whole, no part of which can be affected without tending more 
or less to affect all others, by the means just enumerated, by which these systems 
influence each other. Such are the foundations on which the laws of sympathy de- 
pend, a principle which, as I have endeavoured in a cursory way to point out, more 
than any other, influences the course of all deviations from a state of health. 
THE functions of all the powers of the living animal, we have seen, are mediately 
or immediately excited by agents belonging to inanimate nature. Our organs are 
composed of the same materials with the external world, and can only be immediately 
impressed by agents of their own nature. It is true that the sensorial functions are the 
results of one vital part acting on another, the sensitive nerves on the immediate organs 
of the sensorial power; but the impression these nerves convey is in every instance 
received from the agents of inanimate nature. Here both the agent and the organs 
impressed are of the same general nature, being composed of similar materials, with 
our other organs. The peculiarity of the results depends on vital properties alone 
being employed in their production, whereas in all other functions of the living 
animal, the vital properties of the organ cooperate with the properties of the inani- 
mate materials of which it is composed. Hence it is that its functions admit of being 
immediately excited by the agents of inanimate nature, which, having no properties 
in common with the only properties employed in the sensorial functions, cannot 
directly cooperate in their production. 
Every agent capable of exciting any of the functions of the living animal, we have 
seen, acts as a stimulant or directly debilitating power, according to the degree in 
which it is applied. In the sensitive system their stimulant effect is always followed 
by a proportional exhaustion of excitability ; in the vital system, only when the 
excitement exceeds a certain limit. I speak of a sensible exhaustion, an exhaustion 
beyond that produced by the usual stimulants of life, which, in the vital system, is too 
gradual to be perceived, and as far as relates to any particular stimulant employed 
