40 



PHYSIOLOGY. 



The fibrous matter is produced as the muscular fibre, by the 

 coalescence of cells, in which a secondary deposit takes place. The 

 vesicular by a succession of cells like those of epithelium. 



The chemical constitution of nervous matter is as follows : 



10000 



(Vauquelin.) 



The amount of phosphorus varies at different times of life, and is 

 exceedingly small in idiotcy. According to L'Heritier's analysis, the 

 mi?iim((m is found in infancy, old age, and idiotcy ; and the maxi- 

 mum of water in infancy. 



The nervous structure, like the muscular, is constantly under- 

 going the process of disintegration and renewal, every exercise 

 of this system being accompanied by a loss of its substance, re- 

 quiring new material to compensate for it. This renewal takes 

 place in the intervals of rest. As in the muscular system, its 

 waste is represented by the amount of urea in the urine, so in the 

 nervous system, is its waste represented by the amount of phos- 

 phatic depositions ; the latter being always increased under mental 

 exercise. Persons, therefore, whose mental faculties are much 

 excited, require as nutritious a diet as those who gain their " living" 

 by the sweat of their brows. 



In regard to the regeneration of nervous structure when it has 

 been destroyed, it is now believed, on the authority of Schwann, 

 Steinruch, and Nasse, that the uhite or tubular matter may be re- 

 stored, they having discovered, that in the uniting substance between 

 the ends of a divided nerve, true nerve-fibres may be developed. 

 Perfect restoration, however, does not always take place, owing 

 most probably to the fact, that the central and peripheral portions of 

 the same fibres do not always meet again. 



In regard to the gray or vesicular matter we are not so well in- 

 formed. When a portion of the brain is removed in animals, its 

 place is supplied by new matter ; but whether this becomes true 

 cerebral substance remains to be proved ; from the great activity of 

 its nutritive processes, there seems reason to believe that its loss is 

 repaired by similar matter. 



Those nerve-fibres which originate in the brain, and are distributed 

 to the muscles, have no proper terraination ^ they form loops^ which 

 either return into themselves, or join others formed by the ultimate 

 ramifications of the main trunks. They never anastomose with each 



