488 THE FUNCTIONAL RELATIONS OF THE 



ear is dead to sounds, the eye is blind, and the correspond- 

 ing nostril is similarly insensitive to all odours.* 



But in Hemi-anaesthesia, although the avenues of sense 

 are dosed on one side, the general Consciousness of the 

 individual appears to remain unaft'ected, and his Mental 

 Activity may be but little impaired. This comparatively 

 unaltered mental condition, notwithstanding the absence 

 of direct sensorial stimulation of one Hemisphere, is prob- 

 ably possible only through the intervening activity of the 

 Corpus Callosum — since by means of its fibres the stimulus 

 to the one side of the Brain may be propagated to the other. 

 Both Hemispheres may thus be brought into relation with 

 the various sensorial stimuli emanating from one side of the 

 body; and in this way it is possible for the general Con- 



* The explanation of the loss of the sense of Smell in the cor- 

 responding nostril presents some difficulties. It seems, at first 

 sight, to be altogether at variance with anatomical facts, since the 

 relations of the organs of smell with the hemispheres are, as already 

 pointed out (p. 4ti8), exceptional. They are certainly direct rather 

 than crossed, and it would also tend to contradict existing ana- 

 tomical knowledge if fibres from the Olfactory Ganglia on the 

 road to their ' perceptive centres ' were to be found anywhere in the 

 neighbourhood of the posterior part of the corona radiata. But a 

 very plausible explanation of the loss of the sense of Smell in these 

 cases of Hemi-ansesthesia is to be found, as Dr. Terrier points out 

 ("Functions of the Brain," p. 191), in the well-ivuown experiments 

 of Magendie, as to the functions of the fifth nerve. He ascertained 

 that Smell was lost when the sensibility of the nostril was abo- 

 lished — e._<7., after the fifth nerve had been cut; not because the fifth 

 is the nerve of Smell properly so called, but because " the integrity 

 of the fifth is necessary to the due functional activity of the olfac- 

 tory nerves." If the unilateral loss of Smell in these cases of 

 Hemi-ansesthesia be really due only to the loss of common sensi- 

 bility in the corresponding nostril, then the same loss of Smell 

 ought to occur in Man with those lesions of the ' pons Varolii ' in 

 which the common sensibility of one side of the body is annulled : 

 and the writer's experience leads him to believe that this loss does 

 occur in such cases. 



