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. 



(i) 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. 



(/) 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 C0 2 (?). This is exhaled 

 in less proportion during sleep. 



(I) 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. — The following experi- 



