THE SOURCE OF NERVE FORCE. 77 
and other muscles into play, and the child is otherwise much more 
active than when in utero. 
4, The source of the body heat being central, and the circulation 
of the blood tending to render that of all the parts uniform, it is 
evident, as a simple physical deduction, that the temperature of the 
portion of the body which corresponds to the heated end of the 
thermo-electric couple (which in the theory now under discussion can 
only be the brain), must be lower than that of the blood, because the 
heat supplied to, and developed in it (the brain), is partly employed 
in generating the electric current which is circulating. Dr. John 
Davy noticed that the temperature of the brain of the rabbit was pecu- 
liarly low, considerably below that of the abdominal viscera; his re- 
sults have been considered improbable by some, but have never been 
refuted ; they are strongly in favour of my theory, which, as shown 
above, explains them completely. 
Upon my theory the mechanism of the nervous system may be thus 
summarised— 
The afferent nerves are the conductors to the nerve centres of the 
electric current which is generated by the contact of their peripheral 
ends with the tissues of the cooled skin, which they supply. The 
brain is the largest of the centres towards which the nerve current is 
. directed, the other ganglia forming the smaller. Through these 
centres the currents, as through an elaborate commutator, are split up 
or concentrated’ in a manner not understood as yet, to be directed Page 254. 
along the efferent nerves, which are always so situated as to be beyond 
the reach of external cooling influences. Where an organ acts in any 
way automatically, it. generally has centres of its own, of a size vary- 
ing in degree according to its automaticity, and these minor centres 
are only to a certain extent subject to the influence of the brain. 
As in the working of the electric telegraph, no return or second 
special conductor is required to carry back the current to the point 
from which it started; for where an efferent nerve terminates in a 
muscle, it loses its insulatiug covering, and so is put into indirect com- 
munication with the peripheral sentient nerves through the inter- 
vention of the mass of body tissue generally, which, though its 
resistance is much greater, offers an merpeay larger mass to be 
traversed by the current. 
