THEORY OF A NERVOUS ETHER. 
385 
longer in warm-blooded animals that have died in cold than 
in those that have died in heat. Upon its presence for a con- 
siderable time after death in some animals, 'and for a short 
time in all animals under favouring conditions, I believe to 
depend those post-mortem movements of muscles which Haller 
attributed to the vis insita of muscular fibre. 
The nervous ether is not, according to my ideal of it, in itself 
active or an excitant of animal motion in the sense of a force ; 
but it is essential as supplying the conditions by which the 
motion is rendered possible. It is the conductor, I presume, 
of all vibrations of heat, of light, of sound, of electrical 
action, of mechanical friction. It holds the nervous system 
throughout in perfect tension during perfect states of life. 
By exercise it is disposed of, and when the demand for it is 
greater than the supply, its deficiency is indicated by nervous 
collapse or exhaustion. It accumulates in the nervous centres 
during sleep, bringing them, if I may so speak, to their due 
tone, and therewith rousing the muscles to awakening or re- 
newed life. The body, fully renewed by it, presents capacity 
for motion, fulness of form, life. The body, bereft of it, 
presents inertia, the configuration of “ shrunk death ” the 
evidence of having lost something physical that was in it when 
it lived. 
The theory of a nervous ether comports itself well in respect 
to the refined mechanism of the senses. When the wave of 
atmosphere strikes the tympanum or drum of the ear it 
communicates the vibration to the nervous ether within, and 
so, by the auditory tract, to the central organ, the brain. 
When the wave of luminous ether impinges on the condensing 
retina it communicates the vibration, through the nervous ether, 
along the optic tract, to the brain. When the picture of an 
object is put upon the retina, it is looked at where it is put, 
on the veritable spot where it is focussed, until it evanishes by 
being withdrawn or shut off from the sense. When an im- 
pression is made on the surface of the body, be it made by 
heat, electricity, or mechanical excitation, it is vibrated 
through the ether to the centres of the nervous system ; and 
when an impulse from the centres is conveyed to the muscles, 
it, too, is vibrated through the same medium. 
The ether, as I opine, holds the molecules and cells of nervous 
matter, the ultimate particles of muscles, the corpuscles of blood, 
and probably the ultimate particles of the fibrine of the blood 
in a state of mobility ; it thus passively counteracts the attrac- 
tion of cohesion between particles, and prevents rigidity of 
the flexible or fluid structures of the body so long as they 
live. Being itself a simple physical agent, the nervous ether 
is, I apprehend, influenced in the most signal manner by 
