5/8 NERVOUS SYSTEM 



If the cerebral hemispheres, the olfactory ganglia, the optic lobes, 

 the corpora striata and the optic thalami are removed, the animal 

 loses the special senses of smell and sight and the intellectual facul- 

 ties, there is a certain degree of enfeeblement of the muscular system, 

 but voluntary motion and general sensibility are retained. So far as 

 voluntary motion is concerned, an animal operated on in this way is 

 nearly in the condition of one simply deprived of the cerebral hemi- 

 spheres. There are no voluntary movements that show any degree of 

 intelligence, but the animal can stand, and various consecutive move- 

 ments are executed, which are different from the simple reflex acts 

 depending exclusively on the spinal cord. The coordination of move- 

 ments is perfect unless the cerebellum has been removed. As regards 

 general sensibility, an animal deprived of all the encephalic ganglia 

 except the pons Varolii and the bulb undoubtedly feels pain. In 

 rabbits, rats and other animals, after removal of the cerebrum, corpora 

 striata and optic thalami, pinching of the ear or foot is immediately 

 followed by prolonged and plaintive cries. Physiologists have insisted 

 on the character of these cries as indicating actual perception of pain- 

 ful impressions and as different from cries that are purely reflex. 

 Voluntary movements and cries are observed in persons subjected to 

 painful surgical operations, when incompletely under the influence of 

 an anesthetic, concerning the character of which there can be no doubt. 

 The movements are voluntary, and the cries are evidence of the acute 

 perception of pain ; but such patients have no recollection of any pain- 

 ful sensation. So far as can be judged from what is known of the 

 action of the encephalic centres, the pain under these conditions is per- 

 ceived by some nerve-centre, probably in the pons Varolii, but the im- 

 pression is not conveyed to the cerebrum and is not recorded by the 

 memory. 



Taking all the experimental facts into consideration, the following 

 seems to be the most reasonable view in regard to the action of the 

 pons Varolii as a nerve-centre : 



It is an organ capable of originating impulses that give rise to volun- 

 tary movements, when the cerebrum, corpora striata and the optic 

 thalami have been removed ; and probably it regulates the automatic 

 voluntary action in station and progression. Many voluntary move- 

 ments, the result of intellectual effort, are made in obedience to impulses 

 transmitted from the cerebrum, through conducting fibres in the pons 

 Varolii, to the cord and the general motor nerves. 



The gray matter of the pons Varolii is also capable of receiving 

 painful impressions, which, when all the encephalic ganglia are in- 

 tact, are conducted to and are perceived by the cerebrum and are 



