134 HUMAN PHYSIOLOGY 



weaker and less disciplined individual would do. We 

 say that he exhibits self-control. He does not fly into 

 a passion on moderate provocation; he does not quail 

 when in danger. How shall we express these facts in 

 the language of physiology? We shall probably choose 

 to say that primitive reflexes have been displaced by 

 reactions more recently acquired. The dominant re- 

 actions are those for which the indirect paths by way 

 of the association areas are necessary. We say that 

 the more elementary tendencies are inhibited. This 

 is an obvious principle in matters of good breeding as 

 well as virtue. While it is eminently a feature of human 

 life it is not wholly wanting in the animals that we feel 

 to be real comrades. It is signally displayed by the 

 dog that refrains from biting the child that torments it. 



Language. One of the most remarkable of human 

 powers is that of uttering and comprehending words. 

 A baby is guided by spoken words much earlier than is 

 commonly supposed and long before it reproduces the 

 words that it hears. In course of time it learns to talk. 

 Later the child is taught to read and to write, additional 

 modes of making use of language. When the nervous 

 system is fully developed, every spoken or written 

 word is a stimulus with a definite power to affect it and 

 to secure reactions from it. Brain disease often per- 

 verts or abolishes the use of language. Sometimes it 

 is the ability to speak that is interfered with, sometimes 

 the capacity to act under the guidance of words spoken 

 by others. In the latter case we say that the patient 

 does not ' 'understand " what he hears. This is a psycho- 

 logic inference; what we are sure of is that his conduct 

 is not determined by it. 



There is a small region in the frontal lobe, on the left 

 side in most of the subjects studied, which is reputed 

 to be a speech center. It is close to the part of the general 

 motor area from which the muscles of the vocal organs 

 are supplied. It will be noted that these muscles are 

 not used exclusively in speech. They are employed 



