386 NATURAL SCIENCE [December 
are elucidated. For example: if you have a burning on your hand 
and another on your foot, they will be directly followed by two 
corresponding movements of retraction. 
(h) Reflexes or reflected circulation (see fig. 11)—My 
theory alone can explain the law about the symmetry of reflexes 
(fig. 10), as well as those concerning intensity, irradiation and 
generalisation: this means that as the mechanical excitation grows 
stronger the vibration propagates itself more or less and produces a 
more and more general reaction. The same explanation can prob- 
ably be applied to the phenomena of eccentricity. Any associated 
sensations, for instance the tickling, cough and nausea provoked in 
the pharynx by the pressure of a strange body in the ear, are to be 
explained by an excitation so strong as to radiate to the immediate 
centres of reflection. 
Association of ideas consists perhaps but in the fact of a suc- 
cessive vibration; whenever some elements vibrate, such as stand 
near are set in motion by them. 
“ All our voluntary motions are in general associated, since we 
cannot move a single muscle separately but must needs move a group 
of them.” And why so? Because the vibrations of the anatomic 
elements tend inevitably to radiate, notwithstanding inertia. This 
is observed in capillaries of mercury when examined under the 
microscope. 
(<) Influence exercised by the mass.—Milne-Edwards says 
that the stronger an animal is the more mass its nervous system 
holds. This is made manifest in fig. 12. 
(7) Persistence of impressions.—It is but natural that an 
excitation endowed with some intensity should produce a vibration 
that only dies away gradually. (Fig. 15.) Several optical delusions 
are probably owing to this cause. 
(k) Theory of sleep—The multipolar cells of the centres are 
known to have amoeboid motions and to articulate and disarticulate 
themselves (fig. 19) by the discharge of CO*(?). This is exhaled 
in less proportion during sleep. 
(1) Model applicable to a general conception of a nervous 
system.—I constructed a model in mercury, of the circulation of 
sensations and concomitant phenomena, modifying that (p. 48) 
presented by Luys in his great work on the brain. The most 
curious part of it all is that the vibrations provoked in the con- 
ductors are only reflected with sufficient intensity on the cells 
standing nearer the sensorium, and that they pass from thence to 
the big interior cells. There seems therefore to be no complicated 
mechanism whatever, everything appearing to result from a mere 
question of strength and distance. (Fig. 20.) 
(m) Evolution of the nervous system.—tThe following experi- 
