184 ORIGINAL ARTICLES. 



others, is not a muscle-pain ; it is produced by pressure on the nerves of 

 the muscle-sheath, or of some neighbouring nerve.* And I have proved 

 that no sign of pain is elicited by burning or pricking the muscle itself. 



Now, if we are justified in attributing muscular sensibility to 

 the anterior nerves, it is obvious that these nerves, when irritated, can 

 only excite muscular sensations — no others. It is further obvious that 

 the signs of such sensations must be very different from those of other 

 sensations. Irritation of the root can only produce that sensation which 

 precedes or accompanies adjustment of the muscles, or one of the vague 

 diffusive sensations which the muscles contribute to the general con- 

 sciousness. The direct response to such a sensation would be an adjust- 

 ment of the muscles to which the particular nerves were sent ; but this 

 cannot take place, because the connexion between the nerves and the 

 muscles is cut off. None, therefore, of the ordinary signs could be ma- 

 nifested. But is this a proof that the muscle-nerves are not sensory ? 

 To say so, would be to say that the optic nerve is not sensory, because it 

 may be divided without the animal's manifesting any sign. 



A few paragraphs back, allusion was made to the fact, that one of the 

 nerves of the fifth pair has an "insensible branch" — will not transmit sen- 

 sitive impressions (as the phrase is usually understood) more than a motor 

 nerve will. Claude Bernard says : ' ' Examinant chez le chien le nerf naso- 

 palatin qui va a la membrane muqueuse du nez nous avons ete tres surpris 

 de le trouver en apparence completement insensible, tandis que la branche 

 principale, la sous orbitaire, nous offrait tous les signes d'une sensibilite 

 vive." Here are two branches of the same nerve (both sensory), yet 

 one of them completely without response to the stimulus which ex- 

 cited the others. Did Bernard thence conclude that the naso-palatine 

 was not sensory? By no means. " Cette insensibilite d'un rameau 

 appartenant a la cinquieme paire porterait a penser qu'elle renferme 

 des filet de sensibilite speciale ; Majendie ayant prouve que les nerfs 

 de sensations speciales sont completement insensibles aux irritations me- 

 caniques."\ 



That all nerves may be, and that most are, double in function, the 

 muscle-nerve being predominantly motor, because distributed to motor 

 organs, whereas the skin-nerve is only distributed to the minute mus- 

 cles of the skin, may be inferred from the anatomy of the invertebrata, 

 in whom no double roots exist. Let us examine the ventral ohord of a 

 bee. From each ganglion one nerve-trunk issues, to supply both skin 

 and muscles of each side. The first time I made a preparation of the 

 bee's nervous system, I was forcibly arrested by this unity of motor and 

 sensory nerves. But as I then believed in the classical doctrine, the ex- 

 planation quickly suggested itself that, in the bee, there had not yet 

 taken place that specialization into motor and sensory, which was found 

 in vertebrata. True enough : but what is the specialization ? Is it 

 the introduction of a new kind of nerve, or only the assignment of one 



* Schiff Lehrbuch. tier Physiol., I., 158. f Bernard, II., 95. 



