THE SPINAL CORD 527 



oots contain all the efferent fibers, the posterior or dorsal roots all the afferent 

 iibers. The proofs in support of this view are as follows: 

 Stimulation of the ventral root fibers produces: 



1. Tetanic contraction of skeletal muscles. 



2. Discharge of secretions from glands. 



3. Increase in the degree of the contraction, the tonus, of the muscle 



walls of the peripheral arteries. 



4. Variations in the degree of the contraction, the tonus, of the muscle 



walls of certain viscera either in the way of augmentation or in- 

 hibition. 1 

 Division oj the ventral root fibers is followed by: 



1. Relaxation of skeletal muscles and loss of movement. 



2. Cessation in the discharge of secretions from glands. 



3. Temporary dilatation and loss of the tonus of blood-vessels. 



4. Temporary impairment of the normal activities of the visceral 



muscles from loss of central nerve control; the degree of impair- 

 ment depending on the nature of the viscus involved. 

 'eripheral stimulation of the dorsal root fibers produces: 



1. Reflex excitation of spinal centers, in consequence of which there is an 



increased activity of skeletal muscles, glands, blood-vessels, and 

 visceral walls. 



2. Reflex inhibition of spinal nerve-centers, in consequence of which 



there may be a decrease in the activities of skeletal muscles, glands, 



blood-vessels, and viscera. 



7. Sensations of touch, temperature, pressure, and pain. 

 4 Sensations of the duration and direction of muscle movements, Of 



resistance offered and of the position of the body or of its individ 



parts (muscle sensations). 

 Division of the dorsal root fibers is followed by: 



1 Loss of the power of exciting or inhibiting reflexly the activities of 



spinal nerve-centers and in consequence a loss of the power of 

 exciting or inhibiting the activities of peripheral organs. 



2 Loss of sensation in all parts to which they are distributed. 



The ventral roots are therefore efferent in function, transmitting nerve 

 impulses from the spinal cord to the peripheral organs which exci 



dorsal roots are afferent in function, transmitting nerve impulses 

 o (a] the 



- sff i tiaras 



organs. 



