216 GENERAL VIEW OF THE FUNCTIONS. 



253. The regeneration of Nervous tubuli that have been destroyed, takes 

 place in continuity with that which has been left sound. This may be more 

 easily proved by the return of the sensory and motor endowments of the part 

 whose nerves have been separated, than by microscopic examination of the 

 reunited trunks themselves, which is not always satisfactory. All our know- 

 ledge of the functions of the Nervous System leads to the belief, that perfect 

 continuity of the nerve-tubes is requisite for the conduction of an impression 

 of any kind, whether this be destined to produce motion or sensation ; and 

 various facts, well known to Surgeons, prove that such restoration may be 

 complete. In the various operations which are practised for the restoration 

 of lost parts, a portion of tissue removed from one spot, is grafted as it were 

 upon another; its original attachments are more or less completely severed, 

 frequently altogether destroyed, and new ones are formed. Now in such a 

 part, so long as its original connections exist, and the new ones are not com- 

 pletely formed, the sensation is referred to the spot from which it was taken ; 

 thus, when a new nose is made, by partly detaching and bringing down a piece 

 of skin from the forehead, the patient at first feels, when anything touches the 

 tip of his nose, as if the contact were really with the upper part of his fore- 

 head. After time has been given, however, for the establishment of new 

 connections with the parts into whose neighbourhood it has been brought, the 

 old connections of the grafted portion are completely severed, and an interval 

 ensues, during which it frequently loses all sensibility ; but after a time its 

 power of feeling is restored, and the sensations received through it are referred 

 to the right spot. A more familiar case is the regeneration of Skin, contain- 

 ing sensory nerves, which takes place in the well-managed healing of wounds 

 involving loss of substance. Here there must obviously be, not merely a pro- 

 longation of the nerve-tubes from the subjacent and surrounding trunks, but 

 also a formation of new sensory papillae. A still more striking example of 

 the regeneration of Nervous tissue, however, is to be found in those cases (of 

 which there are now several on record), in which portions of the extremities, 

 that have been completely severed by accident, have been made to adhere to 

 the stump, and have, in time, completely recovered their connection with the 

 Nervous as with the other systems, as indicated by the restoration of their 

 motor and sensory endowments. 



CHAPTER IV. 



GENERAL VIEW OF THE FUNCTIONS. 



1. Of Vital Actions, their conditions, and their mutual dependence. 



254. THE idea of Life, in its simplest and most correct acceptation, is that 

 of Vital Action; and obviously, therefore, involves that of change. We do 

 not consider any being as alive, which is not undergoing some continual alte- 

 ration, that may be rendered perceptible to the senses. This alteration may 

 be evidenced only by the growth and extension of the organic structure, or 

 the development of new parts ; and it may take place so slowly as to be im- 

 perceptible, except by comparing observations made at long intervals. Thus 

 the scaly Lichen, that forms the grey or yellow spots upon old walls, might 

 be thought an inert substance, did we not know that a sufficiently-prolonged 



