THE EDUCATION OF THE NERVOUS SYSTEM. 34! 



changes in the brain are not duplicates of those occur- 

 ring when the sound of it has led to the same reaction. 

 In the two cases the same expressive centres have been 

 directly roused by different sets of fibres, one from the 

 auditory and one from the visual centres, and the 

 secondary revivals have been correspondingly varied. 

 The bearings of these facts are very wide. Among 

 mammals it is a familiar observation that some, like the 

 rat, are dependent on the sense of hearing, or like the 

 cat, on that of sight, or the dog, on that of smell. This 

 means that the mental images which rule these animals 

 are in terms of the dominant sense, and anatomically 

 that the cortical centres for the dominant sense are 

 those best connected with the motor areas. When men 

 are compared, there are possibilities for very wide 

 differences in these arrangements, the eye rather than 

 the ear being generally the dominant organ. Some- 

 thing of this is doubtless due to training, but probably 

 much more to anatomy. It is interesting to note that 

 in these days of printing a large proportion of our 

 second-hand information reaches us through the eye, 

 while in the earlier centuries the ear was the main 

 channel. Further, owing to anatomical peculiarities 

 an individual may be persuasive, with his pen and 

 yet a doubtful orator. Such every-day combinations 

 may be easily explained. The same sensory portions 

 of the brain are not connected impartially with either 

 the centre for the movement of the hand and arm 

 in writing or that for the muscles of phonation used in 

 speech ; but there may be wide differences in this relation, 

 so that the speaking and the writing man are somewhat 

 different persons. The working value of the mental 

 images appears also as dependent on the number and 

 balance of the secondary sensations which accompany 

 them. The greater the number of these the more 



