360 
DR. PHILIP ON THE POWERS OF LIFE. 
In the remaining part of this paper, I am to consider the various relations those 
powers bear to each other in the maintenance of the foregoing systems ; and the way 
in which these systems themselves are so related, as to form the animal body into a 
whole, in which no part can be affected without tending more or less to influence 
every other. 
IN order to ascertain the seat of the power on which muscular contractility de- 
pends, it was necessary in an early part of this paper to enter on the relation which 
subsists between the muscular and nervous systems ; and it appears from what is 
there said, that the nervous influence, whether in its effects on the muscles of vo- 
luntary or involuntary motion, stands only in the relation of a stimulus or directly 
debilitating power to the muscular fibre, according to the manner in which its organs 
are impressed ; a result, I may observe in passing, peculiarly in accordance with all 
the other facts which have been stated respecting the nature of that influence, because 
the same observation, we shall find, applies to all the agents of inanimate nature 
which are capable of influencing the muscular fibre. 
The relation which next demands our attention is that which subsists between the 
organs of the nervous influence and the living blood. 
The first thing, which here strikes us, is that the blood-vessels and nerves uni- 
formly accompany each other ; from which we are led to infer that they cooperate 
in functions of very general necessity. 
The powers of the nervous system properly so called, we have seen, are all of a 
chemical nature. Of this nature therefore must be all processes in which they im- 
mediately cooperate. It is evident that where such powers are employed, to render 
them efficient, materials must be provided on which they may operate, and there must 
also of course be means by which these materials are duly exposed to their action. 
The materials we find in the blood, the means, employed for the purpose of duly 
exposing them to the action of the nervous influence, in the capillary vessels, on 
which, the minute extremities of the nerves, (which we know, from numberless obser- 
vations, are those parts of the nervous system by which its powers are immediately 
applied in the functions of secretion and assimilation, as well as the excitement of 
the muscular fibre,) are distributed. As the central are the only parts of the nervous 
system properly so called, employed in the formation of the nervous influence, the ex- 
tremities of the nerves are the only immediate organs of its powers in all its functions. 
The motion of the fluids in the capillary vessels, as appears from many experi- 
ments related in the Philosophical Transactions for 1815 and my Inquiry into the 
Laws of the Vital Functions, depends on a power which resides in themselves, in no 
degree depending on the power of the heart or arteries, except as far as is necessary 
for the due supply of blood to the latter, which form the reservoirs, from which the 
capillary vessels draw their supply. When in the newly dead animal a ligature is 
thrown round all the vessels attached to the heart and this organ is removed, the 
