is Very acute. There is extreme hyperaesthesia, probably due to 

 nervous anaemia. 



ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. <;;;, 



Physiology of the Spinal Cord and its Nerves. 



I The spinal cord represents: 1. A great conductor whose extent 

 es between the brain and periphery of the body. Along it are 

 transmitted centrifugal as well as centripetal actions; the former 

 carry volitional impulses to the muscles, the latter impressions from 

 the sensitive surfaces to the brain. By reason of the spinal cord 

 having in its composition innumerable nervous cells, it becomes a co- 

 ordinator of the actions which pass over it. 



2. The spinal cord represents a true nervous center. It may be 

 either an important center of reflex phenomena in that its cells unite 

 centripetal fibers with centrifugal ones, or it may possess the role of 



ting as a special center of the special functions. 

 Cord as a Conductor. The law of Bell is enunciated as follows : 

 )/ the roots which issue from the spinal cord, the anterior are those 

 motion and the posterior those of sensation/' 

 This law is very clearly demonstrated by the so-called Muller 

 frog. If the last four anterior spinal roots in the cauda equina of a 

 frog are cut off at the right, and the last four posterior roots are cut 

 off at the left f the animal after recovering from the operation will 

 present interesting conditions. The right lower leg will be para- 

 lyzed; that is, deprived of voluntary motion. The left lower leg will 

 be ancesthetic: that is, deprived of sensation, but still possess motion, 

 eref ore, the anterior spinal roots are motor and the posterior ones 

 nsory. 



Irritation of the posterior roots, or of their central stumps, 

 ermines sensations. These sensations are sharp pains in the 

 gions innervated by the particular nerve. Excitation of the peri- 

 eral stump is without any effect. 



Irritation of the anterior roots, or of their peripheral stumps, 

 termines movements. These movements are of the nature of con- 

 Isive cramps in the particular muscles innervated. Excitation of 

 e central stumps is not followed by any effect. 



Cutting off, or the complete destruction, of the posterior roots 

 uses the loss of tactile, thermic, and painful sensibilities; also of 

 uscular sensation in the parts where they are distributed. Sec- 

 n of the anterior roots wholly paralyzes the muscles innervated by 



