190 



A paper was read, containing " a brief account of a particular 

 function of the nervous system," in which Dr. Marshall Hall detailed a 

 series of experiments tending to prove the existence of a source of mus- 

 cular action distinct from all those hitherto noticed by physiologists : 

 viz. volition, the irritation of the motor nerves in some part of their 

 origin or course, or that of the muscles themselves. The peculiarity of 

 this motion he stated to consist in its being excited " by irritation of 

 the extreme portion of the sentient nerves, whence the impression 

 is conveyed through the corresponding portion of brain and spinal 

 marrow as a centre, to the extremities of the motor nerves." 



The animals experimented on were Salamanders, Frogs and Turtles. 

 In the first of these the tail, entirely separated from the body, moved 

 as in the living animal, on being excited by the point of a needle 

 passed lightly over its surface. The motion ceased on destroying 

 the spinal marrow within the caudal vertebrce. The head of a frog 

 having been removed, and the spine divided between the third and 

 fourth vertebra 1 , an eye of the separated head was touched: it 

 was retracted and the eyelid closed, a similar movement being ob- 

 served in the other eye. On removing the brain these phenomena 

 ceased. On pinching the skin or the toe of one of the anterior 

 extremities, the whole of this portion of the animal moved. On 

 destroying the spinal marrow this phaenomenon also ceased. Precisely 

 similar effects were observed on pinching the skin or toe of one of 

 the posterior extremities ; and on removing the last portion of the 

 spinal marrow this phaenomenon ceased. The head of the turtle con- 

 tinues to move long after its separation from the body : on pinching 

 the eyelid it is forcibly closed ; the mouth is opened and the mem- 

 brane expanded under the lower jaw descends as in respiration. 

 On pinching any part of the skin of the body, extremities, or tail, the 

 animal moves. The posterior extremities and 4ail being separated 

 together, the former were immoveable \ the latter moved on the ap- 

 plication of the flame of a lighted taper to the skin. Those extremities 

 had no connexion with the spinal marrow. All movement ceased in 

 the tail also on withdrawing the spinal marrow from its canal. 



" Three things," Dr. Hall observes, t( are plain from these obser- 

 vations : 1. that the nerves of sensibility are impressible in portions of 

 an animal separated from the rest; in the head, in the upper part of 

 the trunk, in the lower part of the trunk : 2. that motions similar to 

 voluntary motions follow these impressions made upon the sentient 

 nerves : and 3. that the presence of the spinal marrow is essential 

 as the central and cementing link between the sentient and motor 

 nerves.'' 



Dr. Hall then proceeded to adduce another series of experiments 

 still more conclusive. If a frog be made to swallow a watery solution 

 of opium, it becomes affected with symptoms very similar to those of 

 tetanus and hydrophobia ; the body and limbs become rigidly ex- 

 tended ; but besides this state of spasm, the cutaneous nerves be- 

 come extremely susceptive, and the motor nerves extremely excita- 

 tive ; a shake, a touch, a breath of air even, induces spasmodic 

 movements of the body and limbs. A frog made tetanic by opium 



