I .-vi PHYSIOLOGY 



that, as a result of education or training, short cuts are laid down, by means 

 of which reactions adapted to the maintenance of the individual can be ca IT'HM 1 

 out immediately, without thought and without correlated calling up <>l 

 numberless sense impressions. Education in fact consists in laying down 

 these * short cuts ' which, as habits, are the basis of the behaviour of the 

 animal. The more complex the central mechanism and the wider the range 

 of environmental change to which adaptation is necessary, tl;e longer must be 

 the time involved in this process of road-making within the cerebral hemi- 

 spheres. The behaviour of man is therefore a product of many years' 

 training, during which time he is in a state of subjection and unfit, from 

 the absence of habit, to maintain himself as a unit in the human com- 

 munity. The neural short cuts of habit are however of advantage to the 

 individual only in dealing with those events which are of everyday occur- 

 rence. Every novel circumstance must involve a revival of past sense 

 impressions and a calling up of activities of the most diverse portions 

 of the brain in order to arrive at the safest or most advantageous mode 

 of action adapted to the circumstances. Here again the complexity of 

 the process would, by the very delay involved, put a stop to a further 

 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 com- 

 paratively simple auditory and motor processes, which itself may be em- 

 ployed as a unit of thought and brought into connexion 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 lairs, sum- 

 marize 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 representation 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 

 mechanising involved in speech is therefore of interest in its relations to t! e 

 development of the intelligence, and helps us to realize more completely the 

 condition-, which determine the activity and functioning of the cerebral 

 heini>pheivs. Much light is thrown upon this mechanism by the study of 

 disorders in man grouped together under the name Aphasia. 



It has 1 n 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 de- 

 scribed fullv by Broca and referred bv him to a lesion of the third left frontal 

 convoluti m. the patient is unable to speak, although he understands what is 



