68 



the spinal cord, so that the impressions on the left side of the 

 body are transmitted by the right side of the spinal cord, and 

 vice versa. 



2d. That the assumed function of the crossing of fibres in the 

 pons Varolii, and the neighboring parts, does not belong to these 

 fibres, but to the fibres of the spinal cord, all along which they 

 cross each other. 



XXI . ON MUSCULAR IRRITABILITY IN PARALYZED LIMBS, AND ITS 

 SEMEIOLOGICAL VALUE. 



Marshall Hall has published many papers, in which he has tried to 

 prove that the degree of muscular irritability in paralyzed parts maybe 

 used as a means of diagnosis between cerebral and spinal paralysis. 



He calls cerebral paralysis that in which the paralyzed part is de- 

 prived of the action of the brain, but not entirely, or not in the least, of 

 the influence of the spinal cord. On the contrary, he calls spinal 

 paralysis that in which the palsied part is altogether deprived of 

 the action of both the brain and the spinal marrow. The cause 

 of the cerebral paralysis may be seated either in the encephalon or 

 the spinal cord; and the cause of the spinal paralysis may be seated 

 either in the spinal cord or in the nerves. 



In the same individual these two kinds of paralysis may exist 

 together. Suppose a man in whom the brachial enlargement of 

 the spinal cord is considerably softened, and consequently unable 

 to act ; the upper limbs then have a spinal paralysis, and the 

 lower limbs, receiving their nerves from a healthy part of the spinal 

 cord, have only a cerebral paralysis. 



According to Marshall Hall, the cerebral paralysis is attended by 

 augmented muscular irritability, and the spinal paralysis is attended 

 by diminished irritability. He bases this opinion on the following 

 experiments, and on some clinical observations. 



On six frogs he divided the spinal marrow immediately below 

 the origin of the brachial nerves ; and he removed a portion of the 

 ischiatic nerve of the right posterior extremity. He had imme- 

 diately, or more remotely, the following interesting phenomena : 



1st. The anterior extremities alone were moved spontaneously; 

 both posterior extremities remaining entirely motionless when the 

 animal, placed on its back, made ineffectual efforts to turn on the 

 abdomen. 



