626 THE FUNCTION OF THE SPINAL CORD 



either without or with the help of consciousness, especially of volition. 

 In the first case, the control is involuntary or reflex, and in the second, 

 volitional and based upon an accurate conception in consciousness of 

 the state of contraction of our muscles and of the position of our limbs. 

 The Effects of Hemisection of the Spinal Cord.^ — The symptoms 

 following the division of one-half of the spinal cord, are homolateral 

 and contralateral in their nature, i.e., they may or may not be con- 

 fined to the side of the lesion. 



A. Homolateral: 



(a) Motor paralysis, affecting (o) the skeletal muscles innervated by the efferent 

 fibers which leave the cord below the level of the section, and (6) the smooth 

 musculature of the blood-vessels. The latter is made evident by the injection 

 of the blood-vessels of the parts affected and the consequent rise in tempera- 

 ture. The skin becomes dry which fact points toward a secretory motor 

 paralysis. 



(6) Sensory paralysis (anesthesia) in the region of those afferent fibers which 

 enter directly at the seat of the injury. This zone is, of course, limited. Loss 

 of *the muscle-sense and tactile discrimination. The other parts show a cer- 

 tain degree of hyperesthesia. 



B. Contralateral: 



(a) Motor paralysis, negative, 



(&) Sensory paralysis, affecting pain, temperature and tactile localization in 



the region innervated by those fibers which have crossed below the level of 



the lesion. 



This syndrome, consisting of unilateral loss of motion and contra- 

 lateral loss of sensation, is not very evident in the lower animals, but 

 this need not surprise us, because the localization of conduction in the 

 simple spinal cords differs somewhat from that found in the human 

 cord. 2 In addition, we are confronted here by the difficulty that an 

 animal cannot interpret sensory disturbances for us. 



1 Brown-S^quard, Jour, de Physiol., vi, 1863, 124; also see: Petr^n, Archiv fiir 

 Psychiatrie, xlvii, 1911, 495. 



2 Karphus and Kreidl, Pfliiger's Archiv, clviii, 1914, 275. 



