General Principles of Physiology. 107 
after the blood is exposed to the influence of that system that it 
assumes a dark colour in the healthy animal, and as the influence 
of the nervous system on the blood appears to be the means 
employed in the various assimilating processes, this influence 
must possess the power of causing the coagulation of its fibrine. 
These are also the immediate effects of galvanism on arterial 
blood, and it produces these effects more readily than any other 
artificial agent. It also appears from the observations which 
have been made, that an excessive impression communicated 
through the nervous system, is capable of immediately destroying 
the coagulating power of the blood. ‘The same is true of the 
excessive application of galvanism. 
_ It follows from all that has been said, that galvanism, applied 
to the different parts of the animal body while they retain their 
vital power, is capable of the yarious functions of the nervous 
system. We are, therefore, naturally led to inquire whether 
the influence of this system possesses any of the more familiar 
properties of galvanism. We find this question also answered 
in the affirmative. The influence of the nervous system is capa- 
ble of its functions after having been made to leave the nerve, 
and pass through certain conductors of galvanism*. 
It seems at first view surprising that the influence of this sys- 
tem should pass so readily by the ganglionic nerves after their 
division, since we know from every day’s experience that this 
never happens in the spinal or cerebral nerves. But the differ- 
ent circumstances in which these nerves are placed, seem readily 
to explain the difficulty. We know that the power of secreting 
surfaces is increased for the time, if they retain their healthy 
state, by any cause which occasions a greater than usual deter- 
mination of blood to them. The presence of this fluid in such 
surfaces, therefore, solicits towards them a corresponding supply 
of the influence of the nervous system. Thus there is a cause 
soliciting a flow of this influence to the extremities of the gan- 
glionic nerves, which has no existence in the case of the cerebral 
* Philosophical Transactions for the present year. Experiments related 
in the 23d number of the Journal of the Royal Institution, page 18. 
