THE GENERAL CONSTITUTION OF LIVING BEINGS. 1% 
the interposed wire, the nerve-tube, and in the cell placed 
at the other end of the tube the receiving apparatus in- 
tended to record and to translate into a new form the ori- 
ginal impulse. This force, sometimes centripetal, in the 
form of sensitiveness, sometimes centrifugal, in the shape 
of thought, is also both at once as an impulse to movement. 
But the most characteristic thing there is in these acts of 
innervation is, their spontaneousness. The nerve-cells have 
the property of retaining the impression of outward agents 
that have affected them, and of remaining for a greater or 
less length.of time in that condition in which they have 
been artificially placed. Thus, in the physical order, light 
imparts to bodies it has touched for a moment a real actiy- 
ity, and makes them phosphorescent for a longer or shorter 
time. This fitness to keep external impressions stored up, 
which is the privilege almost exclusively of the nerve-cells, 
may continue in the latent state an indefinite time, may at 
length be lost, and not reveal itself promptly except under 
the evoking power of the first impression, or, it may be, 
under that of the surrounding cells, which are in some sort 
new centres of secondary stimulations. Just as we see 
bodies which had become phosphorescent by effect of ex- 
posure to the sun insensibly lose that property, and regain 
it by the help of some other source of phosphorescence— 
heat, for example—so the receptivity of cells may be re- 
stored either under the influence of the first cause, or that 
of some other source of stimulation. Let us remark once 
more, and this is precisely the most important point in 
cerebral innervation, that cells once agitated by contact 
with outward impressions do not stop with this. The 
state in which they find themselves after their impregna- 
tion by the outward impression, and which M. Luys com- 
pares to phosphorescence, spreads on and imparts itself, 
and proceeds, by a succession of intermediate agitations, to 
arouse the beginning of action in new groups of cells situ- 
