THE VITAL AND PHYSICAL FORCES. 
745 
proportional to the expenditure of that force. — Thus a “ correlation ” is distinctly 
indicated between Nervous force and Heat. 
Precisely the same may be said of Chemical Affinity ; for the application of various 
reagents to the nerve-trunks may be made to call into action their peculiar endow- 
ments, whether these be motor or sensory ; whilst, on the other hand, there is ample 
evidence that the chemical properties of secretions may be greatly changed under 
the direct influence of nervous force. 
The power of Light to excite the nervous force is clearly indicated by the influ- 
ence of this agent upon the optic nerve, whose peculiar force is excited by the im- 
pression of light upon its peripheral extremities ; conversely, there are certain phe- 
nomena of animal luminosity, especially among the Annelida, which do not appear to 
be directly referable to chemical change, but which seem to be rather dependent 
upon a direct exertion of nervous power ; vivid scintillations (resembling the lumi- 
nous effects of an electric discharge through a glass tube spotted with tin-foil) being 
excited by any irritation applied to the nervous system of these animals*. 
The relation of Motion to the nervous force is too striking to be passed by. The 
peculiar vital endowments of a nerve may be called into active exercise, as well by 
pinching or pricking it, as by electrical or chemical stimuli; thus by pressure on a 
nerve of common sensation, pain is excited ; by pressure on a motor nerve, muscular 
contraction ; by pressure upon the eyeball, sensations of light and colours may be pro- 
duced in complete darkness ; pressure applied to the meatus of the ear, so as to 
affect the auditory nerve, will give rise to a ringing sound ; and by quickly but 
lightly striking the surface of the tongue, near its tip, with the finger, a distinct 
taste, sometimes acid, sometimes saline, is produced-i-. Conversely, the nervous force 
appears convertible into motion through the medium of the Muscular apparatus, just 
as it excites electricity through the instrumentality of the electric organs of Fishes. 
That the motor force thus generated is always proportional, cceteris yarihus, to the 
* This is the conclusion at which the author arrived some years since, from observations which he made at 
Tenby on a small Annelide (probably a species of Byllis), in which the luminous discharges are seen with ex- 
traordinary brilliancy, when the animal is subjected to irritation, as by slightly pinching or pricking it, or by 
the movement of the water around it. The same conclusion was contemporaneously arrived at by M. de Qua- 
TEEFAGES, from observations made on the Annelida of the coast of France. “ En etudiant, a I’aide du micro- 
scope, de petites Annelides transparents, M. de Quathefages est arrive a decouvrir un rapport curieux entre 
certains phenombnes de phosphorescence animale, et I’influence de I’agent qui determine la contraction mus- 
culaire, et qui, a plusieurs egards, semble tant d’analogie avec I’electricite. II est probable que la lumiere 
plus ou moins vive, que repandent un grand nombre d’animaux inferieurs, ne depend pas toujours de la meme 
cause ; que tantot c’est un phenomene qui accompagne la decomposition des matibres organiques, et que d’autres 
fois c’est le resultat de la secretion d’un liquide particulier ; mais il est probable que, dans un grand nombre 
de cas, la cause de la phosphorescence est entibrement physique, et se lie, comme la contraction musculaire, a V in- 
fluence nerveuse.” — Rapport sur une Serie de Memoires de M. A. de Quateefages, relatifs a I’organisation des 
Animaux sans Vertebres des Cotes de la Manche, par M. Milne-Edwaeds (Annales des Sciences Naturelles, 
Troisibme Serie, tom. i. p. 23). 
+ See Dr. Baly’s Translation of Mullee’s Physiology, p. 1062. 
5 C 
MDCCCL. 
