586 NERVOUS SYSTEM. 



of mechanical movements, which it is unnecessary to detail fully, in the most extraor- 

 dinary mariner. The animal continued to improve, ceased the mechanical movements, 

 and began to fly about, exhibiting timidity when approached, and, in short, seemed, after 

 a time, to have nearly or quite returned to the normal condition. One thing, however, 

 was remarked : the animal never took food (it was probably kept alive by stuffing, as is 

 frequently done in such experiments). After five months, the pigeon was killed. The 

 cranial cavity was found to be filled with a white mass, occupying the place from which 

 the cerebrum had been removed. This mass had the consistence of the white substance 

 of the brain and presented a perfect continuity with the cerebral peduncles, which had 

 not been removed. It had the form of the two hemispheres, presenting a cavity filled 

 with liquid, and a septum. The whole mass consisted of perfect primitive fibres of double 

 contour, and, in their meshes, ganglionic cells. This observation is certainly one of the 

 most remarkable on record, and, from the extraordinary character of its results, it would 

 hardly be accepted for a moment, but for the established reputation of Prof. Voit. As 

 it is, such an observation demands full confirmation. It is well known, to all who have 

 been in the habit of extirpating the cerebral lobes, that it is absolutely necessary to 

 remove every portion of their substance, in order to obtain uniform results, and that 

 this is accomplished sometimes with considerable difficulty, In demonstrations to a 

 medical class, we have frequently verified this fact, and have observed recovery, more 

 or less complete, when but a small portion of the posterior lobes escaped. This criticism 

 upon the remarkable observation just detailed is made by Vulpian, and its pertinence 

 will be recognized by every practical physiologist. We have only to study the experi- 

 ments first made by Flourens, to learn how, in the lower animals, a part of one of the 

 great central ganglia may gradually assume the function of the whole, after this function 

 has been interrupted by the first mutilation. "We have cited the essential points in this 

 observation because it has been so extensively commented upon by physiologists, but it 

 is far from establishing the principle that a great nervous centre, like the cerebrum, may 

 be anatomically and functionally regenerated after complete extirpation. 



The general results of the experiments of Masius and Vanlair upon the regeneration 

 of parts of the spinal cord in frogs, after loss of a small portion of its substance, show 

 that such reparation may take place and be attended with restoration of function. The 

 formation of cells precedes the development of fibres, and voluntary motion appears in 

 the parts situated below the lesion, before sensation. There are no instances on record 

 of such regeneration in the human subject or in the warm-blooded animals. 



Motor and Sensory Nerves. 



The physiological property of nerves which enables them to conduct to and from the 

 centres the impressions, stimulus, force, or whatever the imponderable nervous agent 

 may be, is one inherent in the tissue itself, belonging to no other structure, and is 

 dependent for its continuance upon proper conditions of nutrition. So long as the nerves 

 maintain these conditions, they retain this characteristic physiological property, which 

 is generally known under the name of irritability. 



Aside from the special senses, the sense of temperature, and the appreciation of 

 weight, it is known to every one that, through the nerves, we appreciate what are 

 called ordinary sensations and are enabled to execute voluntary movements. If a nerve 

 distributed to a part endowed with sensation and the power of motion be divided, both 

 of these properties are lost and can only be regained through a reunion of the divided 

 nerve. Again, it is equally well known that, if such a nerve be exposed in its course 

 and irritated, violent movements take place in the muscles to which it is distributed, 

 and pain is appreciated, referred to parts supplied from the same source. These facts, 

 which were fully appreciated by the ancients, show that the general system of. nerves is 

 endowed with motor and sensory properties, the question being simply whether these be 



