496 GENERAL ANATOMY. 



the nervous filaments are larger in it, and that it is easy to fill 

 the neurilematic canals. But, this nerve differs from the 

 others by its canals being separated by common partitions 

 which are detached from the interior of the general sheath. 

 The structure of the nerves has however also been observed 

 in other nerves: it is especially in those of the muscles where 

 the filaments are more distinct than in the nerves of the senses 

 or of the skin, that these observations have been made. 



782. Reil, to whom we owe almost all that is known about 

 the structure of the nerves, has well indicated the means by 

 the aid of which this structure may be observed. By washing 

 the nerve with water and nitric acid, at the end of a certain 

 time, the neurilema is entirely destroyed, and there remains 

 medullary filaments which may. be seen crossing each other, 

 resting against each other, nearly like the optic nerves in their 

 commissure. On the other hand, plunging a nerve into ley, 

 which may be regarded as an alkaline solution of subcarbonate 

 of soda, the medullary substance is destroyed, and the neuri- 

 lematic sheaths are obtained. To hinder them from becoming 

 effaced, they may be filled with air: which is very easy, by 

 forcing this fluid into one of them, since they all communi- 

 cate with each other; the nerve is then tied at its two ends: 

 when dried in this state, it presents, on being cut, a multitude 

 of little canals opening into each other, which gives it the 

 aspect of the interior of a reed. These observations, which 

 have been repeated many times, after Reil, demonstrate the 

 two different substances of which the nerve is composed. 



The observations of Home, upon the optic nerve, have 

 shown that the medullary filaments of which it is composed, 

 augment in number, and diminish in volume, from the origin 

 to the termination. 



783. The nerves have little or no elasticity; they have no 

 sensible motion, either of oscillation, or vibration, when irri- 

 tated in the living animal. The irritation of a nerve produces 

 severe pains, and brings convulsive contractions in the muscles. 



784. The functions of the nerves are to conduct sensation 

 and motion. They transmit, with incalculable velocity, voli- 

 tion from the nervous centre to the muscles, and convey to 



