DR. PHILIP ON THE POWERS OF LIFE. 
369 
It is a law of the animal economy, amply illustrated by the phenomena of 
disease, that when an impression influencing the system generally is, by previous 
debility or any other cause, directed to a particular part, its operation is diverted 
from all others. Now it appears from a thousand phenomena that the suffering 
of the sensitive system, referred to any particular part, is sufficient, under certain 
circumstances, in consequence of the influence of the central organs of the sen- 
sitive, over those of the vital system, to direct to it the effects of derangement 
excited in the latter. Thus even a diseased organ will often regain its healthy state, 
when the disease has spread to another, particularly if in the latter, it takes deeper root, 
if I may use the expression. It is a daily occurrence for a disease of function to be 
finally removed by a disease of structure being established in another organ. Hence 
the good effects of artificially exciting disease in external parts to relieve those more 
immediately essential to life ; and the still mere salutary effect, when the laws of our 
frame themselves produce the same effect, because here it is the uninfluenced result 
of those laws, whereas in the former case their tendency is constrained by artificial 
means. Thus for example it is that the inflammation of a gouty joint or other ex- 
ternal disease often relieves the derangement of a vital organ, and that artificially re- 
pelling this effort of the constitution to save a vital part, has so often proved fatal. 
On the facts that the central organs of the vital system directly influence the func- 
tions both of the vital nerves and of the vessels of every part, while those of the sen- 
sitive system have no direct influence on either, many of the phenomena of disease de- 
pend ; because it is only in proportion as these nerves and the vessels of the part are 
influenced, that any disease of the part itself exists, and consequently that there is any 
tendency to derangement either of function or structure in the part ; of function alone 
if the nerves alone are affected, of structure also as soon as the vessels partake of the 
disease. Hence it is that the tendency to change of structure, except where it takes 
place by imperceptible degrees, is, cceteris paribus, always proportioned to an inflam- 
matory tendency which may be detected in the part, this tendency being the first 
indication that the vessels partake of the disease ; and hence the importance of care- 
fully watching and checking its approach, if the part be one essential to life, in all 
cases of deranged function of, or even of painful sensations referred to, particular parts. 
EXTENSIVE as the foregoing relations of the vital and sensitive systems are, they 
are not the only ones. To determine the whole of them it is necessary to review the 
functions of the more perfect animals, and in particular correctly to ascertain the 
line of distinction between the functions of the two systems ; in order to determine 
whether there be any beside those just pointed out in which they cooperate, and 
which consequently contribute to their dependence on each other. 
I made many experiments with a view to draw the line of distinction between the 
vital and sensitive functions ; and that the result might be the more certain, the 
attempt was made by two sets of experiments, conducted on different principles. By 
MDCCCXXXVI. 3 B 
