THE GENERAL CONSTITUTION OF LIVING BEINGS. 73 



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 activ- 

 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- 



