388 BIOLOGY. [Book vi. 



From the striated bodies travel descending fibres, which en- 

 counter on their path the motory cells of the spinal marrow, 

 then radiate thence into the nervous cords and threads, and 

 end their journey at the contractile elements, the elements of 

 muscular tissue. 



We can thus follow along its whole anatomical career and in 

 all its physiological metamorphoses the impression received by 

 the terminal extremity of a sensitive nervous fibre. If, for 

 example, a hard body strikes violently any point of the cutaneous 

 envelopment, the molecules of the nervous fibres, harshly 

 touched, enter from point to point into vibration ; the shock com- 

 municates itself first of all to the cells of the marrow, then to 

 those of the optical layers, then to the cells of the cerebral cir- 

 cumvolutions. No doubt this shock is modified in a fashion not 

 known in its passage through these nervous centres. Let this 

 be as it may, on reaching the superficial cells of the circumvolu- 

 tions, the shock, the vibration, the molecular movement, what- 

 ever may be the form thereof, awakens in these cells an altogether 

 special phenomenon, a phenomenon of consciousness, or sensation. 

 But we are only yet at the h^lf of the circuit. The sensitive 

 nerves which have incurred the shock communicate in their turn 

 the agitation to the subjacent cellular strata. These last cells, a 

 little larger than the superficial or sensitive cells, a little smaller 

 than the deep, or motory cells, are probably the thinking cells. 

 In these the molecular shock is transformed into ideas. The 

 ensemble of these thinking cells constitutes the soul of the 

 organism. They take account of the causes of pain, com- 

 bine the means of preventing the return thereof, and their 

 decision, communicated to the deepest cortical layers, is there 

 metamorphosed into volitions. In effect the deep cells of the 

 cortical layers are motory, or rather volitive. They ordain the 

 muscular movements necessary to prevent the return of the 

 painful shock, and to ward off danger. The comn^and is 

 transmitted along the convergent central fibres, then through the 

 cells of the striated bodies and of the spinal marrow. Finally, 



