100 LECTURE IV. 



sphere may, for a certain time at least, perform all requisite 

 functions. All that is observed^ is that the cerebral activity is 

 sooner exhausted than in the uninjured brain, so that it is 

 merely the quantity and not the quality of the function which 

 is affected. Some physiologists have, not unreasonably, asserted 

 that such an interchanging of activity of the two cerebral hemi- 

 spheres may and does occur also in the living man, and that one 

 hemisphere may, to a certain extent, go to sleep and refresh 

 itself, whilst the other half is in a state of activity. The facts, 

 however, upon which this assertion is based, are, as yet, insuf- 

 ficient for the establishment of such a theory. 



Neither wounds in the head nor cerebral diseases have hith- 

 erto yielded satisfactory evidence as regards the locaHsation of 

 the intellectual faculties in individual parts of the cerebrum. 

 The question has been much discussed whether speech, or, 

 rather, the capacity for producing articulate sounds expressing 

 thoughts, is localised in the anterior lobes of the brain, and 

 cases have been adduced in which a morbid condition of those 

 parts was concomitant with loss of speech. But the fact that 

 one hemisphere may act vicariously for the other, has been lost 

 sight of, and also that it is but rarely that both hemispheres 

 are equally affected. This, however, is clearly the requisite 

 condition for estimating such a case, for that function which is 

 destroyed by disease on one side may be preserved on the other, 

 and, though sooner exhausted, would, for a time, be performed 

 in its integrity. Cases are by no means rare of persons hav- 

 ing lost a quantity of cerebral substance from one hemisphere 

 by wounds, and who, though exhibiting no actual diminution 

 in their intellectual functions, were compelled frequently to 

 rest after any mental exertion, as their mental energy was 

 sooner exhausted. 



Since direct observations yield but scanty results, we may 

 be permitted to appeal to conditions which may indirectly con- 

 tribute towards the elucidation of the question. The results 

 of such investigation certainly do not possess the same validity 

 as those drawn from direct observation. Still, they are of 

 some value and should not be neglected. 



There are normal conditions in which certain parts of the 



