158 THE HUMAN BODY 



An interesting thing about these language association areas is 

 that they seem to be confined to one of the cerebral hemispheres; 

 in right-handed people the left hemisphere contains them, and 

 in left-handed people they occur in the right hemisphere. It has 

 been observed, moreover, that the development of right or left- 

 handedness in infants is coincident with their learning to use 

 language. Just what the relationship between the two properties 

 may be is not clear. 



Impairment of a sensory language area results in word-deafness 

 or word-blindness; the sounds are heard, or the words are seen, 

 but they are without meaning because the power to associate 

 language with concepts is affected. When motor language areas 

 are injured the power of expression is lost. The commonest of all 

 these abnormalities is the loss of power to use spoken language, a 

 condition known as motor aphasia. The sufferer from this con- 

 dition knows what he wants to say but is unable to recall the 

 words by which to express his ideas. Embarrassment often gives 

 rise to a momentary inhibition of the motor aphasia region, re- 

 sulting in the same inability to recall the needful words. 



Since all our mental processes are dependent on language, im- 

 pairment of the language areas would be expected to lower the 

 whole mental power. This appears to be the case in most sufferers 

 from this condition. 



There is no evidence that any species of animals except the 

 human species possesses the power to use language. This differ- 

 ence sets man sharply apart from the animals most nearly ap- 

 proaching him in intelligence. 



Consciousness. This is a phenomenon that we all recognize 

 as existing in ourselves and as accompanying most if not all of 

 our cerebral activities. That it is present when the cortical cells 

 are actively functioning and absent when they are inactive is 

 indicated by the fact that any treatment, such as anaesthesia, 

 which depresses nerve-cells, tends to abolish consciousness. It 

 is a phenomenon whose nature is wholly unknown, and for whose 

 existence, even, there is no objective evidence. We cannot prove 

 that any lower animal has the same sort of consciousness that we 

 have. We can only suppose from the general similarity of their 

 cerebral processes to ours that this particular phenomenon is 

 also in them as in us. As we go down the animal scale where 



