356 ORIGIN AND CIRCULATION OF THE NERVOUS INFLUENCE. 
duce electricity, or, at least, that their capability of doing so 
is probable. But the very opposite of this is the case, there 
being scarcely a tissue of the animal system less likely to 
originate electricity than the substance of which the brain and 
spinal marrow consists. 
I beg to suggest a source from whence this electricity may 
be derived, which appears to have at least this advantage, 
that the electric fluid in sufficient quantity may be obtained 
from it, — namely, the chemical action which is constantly 
going on in the change of arterial into venous blood. Other 
chemical actions in the system may assist in producing the 
requisite amount of electricity; but, for the sake of simplicity, 
it may be as well to confine our attention at present to the 
one which is probably the most important. 
In every chemical action galvanic electricity is evolved; a 
large amount must therefore be produced in the animal 
system by the change of arterial into venous blood. The 
following is a condensed view of what is now generally ad- 
mitted to be the nature of the change referred to. The blood, 
after being exposed to the influence of the atmospheric air in 
the lungs, acquires a large amount of oxygen, so that the 
iron which it contains exists in the highest state of oxygena- 
tion as the peroxide. On reaching the capillaries, the peroxide 
of iron comes in contact with carbon, which attracts a portion 
of the oxygen ; by this the peroxide is reduced to the state 
of protoxide of iron, and the carbon is converted into car- 
bonic acid. The protoxide of iron and the carbonic acid, 
thus produced, immediately unite, forming the carbonate of 
iron. 
It is quite clear that by these combinations galvanic elec- 
tricity must be produced in great abundance ; and as iron 
does not enter into the composition of any of the tissues or 
secretions of the body, it is probable that the production of 
electricity is the only purpose of this mineral existing in the 
blood in such quantity. 
The chemical changes referred to are effected in the vessels 
situated between the termination of the arteries and the 
commencement of the veins. Now it is demonstrable that 
wherever arteries terminate and veins begin, there also are 
nerves distributed, and as these consist of afferent and 
efferent fibrils, which have been proved to be conductors of 
electricity, we have only to suppose that the galvanism set 
free by the chemical action is taken up by the afferent 
nerves, and passing through the nervous centres, is returned 
by the efferent nerves to the same point, and thus a continued 
electric circuit is established, every modification of which 
must promote or retard the chemical change, and so influence 
