472 STUDIES IN ADVANCED PHYSIOLOGY. 



While this relation of cause and effect is absolutely clear, it 

 is equally clear that there is not a bit of similarity between 

 the neurosis and the psychosis. In other words, vibrations 

 in the internal ear, or even the nervous impulses which 

 such vibrations produce are absolutely different in kind from 

 those psychological sensations which we designate as sound, 

 and there is clearly no similarity between an ethereal vibra- 

 tion or the stimulation of a rod or cone in the eye and what 

 we psychologically call light. Between the two there is a 

 chasm that cannot at present be bridged, and so all at- 

 tempts at explanation are useless and out of place. To 

 prove the assertion that there is no similarity in essence be- 

 tween physical light and psychological sensation of light one 

 needs only to be reminded that the psychological sensation 

 of light can easily be produced when no physical light is 

 present. One needs only to be struck on the head or to 

 have the optic nerve stimulated, electrically or otherwise, to 

 perceive in the most emphatic and clearest way sensations 

 interpreted as those of light. The stimulation of the audi- 

 tory nerve will produce a ringing noise in a perfectly 

 quiet medium. 



To summarize, then, sensations differ in their modes or 

 modality, a difference caused by the centers in the brain to 

 which they go. Of the sensations of a separate and distinct 

 mode, such as those of sight, there may be distinctions in 

 quality, such as those of red, green or blue lights, or in in- 

 tensity, such as a strong or faint light. There may be dif- 

 ferent qualities which we recognize as differences in touch, 

 or different intensities which we recognize in loudness or 

 softness. The modality of a sensation is determined by the 

 brain center to which the nerve goes, while the quality and 

 the intensity of the sensations of the single modality are 

 normally determined by the end organ itself. 



THE DEVELOPMENT OF THE SPECIAL SENSES. 



From an anatomical, especially an embryological point 

 of view, it is at once apparent that the special sensations 



