DR. PHILIP ON THE POWERS OF LIFE. 
365 
hand, tending to exhaust excitability, and extreme cold, on the other, to render us 
less capable of excitement. 
While considering the laws of excitability it is necessary to bear in mind an essential 
property of all those agents which are capable of calling it into action, and which has 
demanded less attention than its great importance in the treatment of disease demands. 
There is no agent capable of influencing either of the two systems into which the 
functions of the living animal arrange themselves, whether it be such as makes its 
chief impression on the mind or body, which is not capable of acting either as a 
stimulating or directly debilitating power according to the degree in which it is ap- 
plied. There is none which may not be applied in so small a degree as to act as a 
stimulant, and in so great a degree as to act as a directly debilitating power. The 
most depressing passion in a comparatively small degree will excite, the most ex- 
citing in an excessive degree directly debilitate ; and the same stimulus by which 
either the nervous or muscular fibre is directly excited, will by its excessive application 
directly deprive it of power. I know of no exception to this law. All medicines 
within their stimulant range excite, and unless the excitement exceeds the degree 
which produces no correspondent depression, (for such a degree of excitement is com- 
patible with the laws of the vital though not with those of the sensitive system *,) it 
acts as a permanent tonic. All, beyond their stimulant range, act as directly, and 
although within that range, if of a certain intensity, as indirectly debilitating powers 
with respect to both systems^. 
IT is evident from many facts, stated in my papers on the Nature of Sleep and 
Death, that each of the foregoing systems is a whole, which cannot be influenced in 
any one part without a tendency to be affected in all others ; a property which perhaps 
more than any other influences the progress of their deviations from the healthy state; 
for every part more or less feeling the change effected in any one, if there be any from 
accidental causes more liable to disease than the rest, this part particularly feels the 
cause which operates on all ; and, as I shall soon have occasion to point out more 
particularly, is even the means of diverting its effects from every other part. Thus 
it is that diseases of continuance become complicated, and that an affection, attended 
with little risk in the part first impressed by the offending cause, often becomes 
formidable by its secondary effects. 
* My paper on the Nature of Sleep in the Philosophical Transactions for 1833. 
t See what is said on this subject in my treatise On the Influence of Minute Doses of Mercury in restoring 
the Functions of Health, and my Gulstonian Lectures on the more obscure affections of the Brain, also in the 
recapitulation at the end of this paper. All my Treatises, to which I have occasion to refer, are more or less 
founded on the principles here recapitulated ; and consequently in them more or less copious references to the 
facts, on which these principles rest, became necessary. In order to arrive at the conclusions of the present 
paper, it was necessary to state the whole of those facts with their various bearings, which I have done in as 
concise a manner as the requisite perspicuity appeared to admit of. In the less familiar parts of the subject, 
it requires some care to avoid being misunderstood. 
