512 PHYSIOLOGY 



rise in intellectual, i.e. associative, capacities, were it not for the 

 invention of SPEECH. 



In speech we have a symbolism which acts as an economy of 

 thought or of cerebral activities. An object, such as a table, with 

 its associated properties of colour, consistence, spatial extension, 

 and resistance, with the connoted acts associated with its use, can 

 now be evoked as a word, involving comparatively simple auditory 

 and motor processes, which itself may be employed as a unit of 

 thought and brought into connection with other words, each of which 

 in the same way is the symbol for a whole series of sensory and motor 

 processes! The training of the cultivated man consists in a constant 

 extension of the range of this symbolism, and the acquisition of words 

 including wider and wider groups of neural processes, so that finally 

 we arrive at those short verbal collections which, as the so-called 

 natural laws, summarise the experience not only of the individual 

 but such as is common to the whole race of mankind. All science 

 may in fact be regarded as an extension of the process of representa- 

 tion of neural experience in symbolic shorthand, which in the child 

 begins with the utterance of such a simple word as ' mamma,' and from 

 which speech has arisen. A study of the nervous mechanisms involved 

 in speech is therefore of interest in its relations to the development 

 of the intelligence, and helps us to realise more completely the 

 conditions which determine the activity and functioning of the 

 cerebral hemispheres. Much light is thrown upon this mechanism 

 by the study of disorders in man grouped together under the name 

 Aphasia. 



It has been usual to divide the disorders of speech known as aphasia 

 into various groups, as follows : 



(1) Motor aphasia, or aphasia of Broca. In this condition, which 

 was described fully by Broca and referred by him to a lesion of 

 the third left frontal convolution, the patient is unable to speak, 

 although he understands what is said to him and has been stated 

 to suffer from no impairment of his intelligence. 



(2) Sensory aphasia, or aphasia oj Wernicke. This condition was 

 connected by Wernicke with the existence of lesions in a fairly wide 

 area, known as the area of Wernicke, which involves the supra- 

 marginal and angular gyri and the hinder portions of the first 

 and second temporo-sphenoidal convolutions. In these cases there 

 may be limited power of speech, but there is serious impairment of 

 the intelligence and especially of the power of appreciation of spoken 

 words, so that the patient does not understand what is said to him. 

 This condition may or may not be attended with alexia, loss of power 

 co read. Any impairment of the motor processes of speech which 

 is present is due rather to the inability of the patient to appreciate 



