CENTRE FOR SPEECH. 621 



subject to variations analogous to those observed in the "personal equa- 

 tion." 



Centre for the Expression of Ideas in Language. The location of this 

 centre depends entirely upon the study of cases of disease in the human sub- 

 ject. It is evident that there must be a comprehension of the significance of 

 words, the formation of an idea more or less complex, and a co-ordinate action 

 of the muscles concerned in speech, as conditions essential to expression in 

 spoken words. One or more of these conditions may be absent in cases of 

 disease ; and the general absence of the power of verbal expression, when 

 this depends on cerebral lesion, is known as aphasia. This is quite different 

 from aphonia, which is simply loss of voice. If the comprehension of the 

 meaning of words be absent, the individual is incapable of receiving ideas 

 expressed in language. In cases of aphasia it often is difficult to determine 

 this point. In certain cases it is possible that the individual may under- 

 stand what is said and may form ideas to which he is unable to give verbal 

 expression. In such instances he can neither speak nor write. There are 

 certain cases in which the written or printed words convey no idea, while 

 spoken words are understood, but there is no loss of intelligence and words 

 are spoken without difficulty. This condition is called word-blindness. If 

 there be simple want of co-ordination of the muscles concerned in speech, 

 words are spoken which may have no connection with the idea to be con- 

 veyed, but the individual may be able to express himself in writing. This 

 condition is known as ataxic aphasia. The inability to express ideas in writ- 

 ing is called agraphia, and this is usually an indication of the condition 

 known as amnesic aphasia, in which it is impossible to put ideas into words 

 in any way. Persons affected with purely ataxic aphasia may understand 

 and write perfectly, but they can not read aloud or repeat words or sentences 

 spoken to them. In cases of simple amnesic aphasia, patients can sometimes 

 repeat dictated words. In cases in which hemiplegia is marked, the aphasia 

 usually is ataxic. In cases in which there is no hemiplegia, the aphasia usu- 

 ally is amnesic. The ataxic and amnesic forms of aphasia may be combined. 

 A full description, however, of the many and varied forms of aphasia would 

 be out of place in this work. 



In 1766, Pourfour du Petit reported a case of aphasia, with lesion of the 

 left frontal lobe of the cerebrum, in which the patient could pronounce 

 nothing but " non" 



Marc Dax (1836) indicated loss or impairment of speech in one hundred 

 and forty cases of right hemiplegia. These observations attracted little at- 

 tention, until 1861, when the subject was studied by Broca. Since then, 

 many cases of aphasia with lesion of the left frontal lobe have been reported 

 by various writers. In 1863, M. G. Dax, a son of Marc Dax, limited the 

 lesion to the middle portion of the left frontal lobe. It was farther stated, 

 by Broca and Hughlings Jackson, to be that portion of the brain nourished 

 by the left middle cerebral artery (the inferior frontal branch). According 

 to recent observers, the most frequent lesion is in the parts supplied by the 

 left middle cerebral artery, particularly the lobe of the insula, or the island 



41 



