400 SEA-SIDE STUDIES. 



ences of colour ; although the nervous impression may 

 be equal in the two, it will be less homogeneous in the 

 artist, whom we may supjDose to have a more special- 

 ised retina. 



The assumption that fibres are organs of conduction 

 at all, may be disputed ; nor, if what was previously 

 said respecting the identity of cell and fibre, in ulti- 

 mate structure, and of the identity of ganglion and 

 tube, be admitted, can we allow the old hypothesis of 

 conduction to be more than a metaphor. The notion 

 of an actual conduction taking place, analogous to the 

 conduction of electricity, is extremely doubtful to me. 

 If the nerves are identical in elementary structure with 

 the ganglia, and consequently j^ci^^ticijMte in the pro- 

 perties of the ganglia, they can no longer be regarded 

 as the conducting-rods of the battery, but as essential 

 parts of it. In our present ignorance of the true pro- 

 cess we may continue to employ the metaphor of con- 

 duction, if we understand by it simply the change which 

 follows when a nerve is affected ; and we may then 

 gain some glimmering of the special function of the 

 fibres, and the meaning of their increase with old age. 

 Nerve-tissue in its earliest stage is wholly without 

 fibres ; as development advances, the fibres multiply.* 

 In old age the brain hardens from excess of fibres, as 

 the bones harden from excess of lime ; so that what 



* Not till the beginning of the fourth month of the human embryo 

 are fibres discoverable in the spinal chord. — Tiedemann, Anatomie du 

 Cerveatt, p. 126. When the fibres first make their appearance in the 

 brain, I know not, but in the brains of a new-born puppy and kitten I 

 could find no trace of them. Indeed^ the naked eye showed that no 



