Page 253. 
76 THE SOURCE OF NERVE FOROE. 
able of being generated between soft tissues of different composition or 
structure, such as the extremities of the sentient nerves and the corium 
in which they are embedded. 
Although Magnus was not able to produce any thermo-electric 
current between fluid metals, his experiments are not in any way con- 
clusive against the possible existence of such currents between dif- 
ferent tissues ; the subject is in a position for actual demonstration, 
no doubt, and I much regret that as yet I have not had opportunities 
of attempting to prove or disprove it. Notwithstanding this, some of 
the circumstantial or collateral evidence is so strong, that, without any 
direct proofs, I feel justified in assuming its correctness. The follow- 
ing points strongly favour my theory. 
1. Within certain limits, which are those ra which the body is 
most generally exposed, the energy of the individual (which must be 
closely related to the supply of nerve force) is greater as the tempera- 
ture of the air is less. On a cold day, in a cold air, there is more will 
and power to work physically than in hot weather, in a hot air, during 
which languor is a prominent feature. In a paper published in this 
Journal* I have proved that the circulation through the skin in man 
varies according to the temperature of the atmosphere, and that when 
70° F. of the air is reached, perspiration commences. Consequently 
by this means a difference of about 30° F. is always maintained in 
health between the surface and the interior; and exposure to the 
highest temperatures of the Turkish bath, when continued for some 
time, does not disturb this condition. But a hot-water bath is fol- 
lowed by very different consequences; if the body and face be im- 
mersed in one of 100° F., and breathing be performed through a tube 
projecting from the mouth to the surface, as I have tried, faintness, or 
loss of nerve power, comes on very rapidly, and is it not because the 
temperature of the surface is raised to that of the interior? At all 
events this explanation is as reasonable as any other. This faintness 
is soon recovered from on the reapplication of cold to the skin. 
2. The effect of muscular exercise is to raise the temperature of 
the body, and so to increase the difference of temperature between it 
and the external air; and when great muscular exertion has to be sus- 
tained, as in rowing, most of the clothes have to be removed in order 
to allow of the rapid cooling of the surface, the necessity for which is 
keenly felt. 
3. During intra-uterine life the active chemical changes going on 
in the body of the foetus maintains its temperature at a slightly higher 
point than that of the mother; but immediately after birth the nerve 
force generated by the cooling of the surface brings the intercostal 
* Supra, p. 87. 
