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simple external conditions. It is influenced by variations of 
heat and cold, is increased in volume by heat, is contracted or 
condensed by cold ; it is influenced by atmospheric pressure ; it 
is influenced by electrical conditions of the air ; the inductive 
effects of electricity on the muscles of living animals are due, 
as it seems to me, to the disturbance excited by the electrical 
action upon the animal atmosphere; nay, I conceive, we 
ourselves are rendered conscious of the changes of external 
conditions — of heat, of cold, of variations of the barometrical 
pressure, of electrical storms — by the sensible fluctuations of 
the atmosphere within us. 
Through the nervous ether, itself a gas or vapour, other gases 
or vapours may readily and quickly diffuse, and by such dif- 
fusion may so modify the physical characters of the natural ether 
as to lead to modifications of nervous function. Thus those 
vapours which, being diffused into the body, produce benumbing 
influence — as the vapours of alcohol, chloroform, bichloride of 
methylene, ethylic ether, and the like — produce their benumb- 
ing effects because they are not capable of taking the place of 
the natural ether into which they diffuse : they interfere, that 
is to say, with the physical conduction of impressions through 
what should be the pure atmosphere between the outer and 
the inner world. A dense cloud in the outer atmosphere shall 
shut out my view of the sun ; a cloud in the inner atmo- 
sphere of my optic tract shall produce precisely the same 
obscurity. 
Pain is the result of rapid vibration of the nervous ether ; 
and pain, whether it be called physical or mental, is the same 
event. The so-called physical pain, that which comes from a 
blow or a cut, is excessive vibration, more than the brain can 
receive. The so-called mental pain is excessive vibration carried 
through the senses to the centres, or excited in the centres 
and carried to the outlets of the body for relief. 
It is, I think, no figure of speech to say that nerves bleed 
— no figure of speech to affirm the phenomena of nervous 
exhaustion, of nervous collapse, of nervous strain and of 
nervous overstrain. Under mental labour or emotion nerves 
bleed as vessels do — bleed not blood in mass, but the richest 
product of blood. Under violent shock the whole nervous 
atmosphere is thrown into vehement vibration, the heart is held 
fixed by the commotion, and the failure of animal force is 
followed by sudden and overwhelming prostration. These are 
all clear physical phenomena. A feeble animal chemistry yields 
a feeble nervous tension, a powerful chemistry or action pro- 
duces over-tension. 
The infliction of physical pain is followed by the shriek, the 
sob, the moan, or the hard setting of muscle : the shriek, the 
