160 THE SENSES. 



What subjective sensations of hearing occur ? 



They may be due to disturbances of the auditory apparatus or 

 to abnormal conditions of surrounding organs. Thus, buzzing or 

 ringing in the ears may result from the hypersernia of the parts 

 and exaggerated rush of blood, or from a defect in the circulating 

 apparatus (as by an aneurism), or from disease in the auditory 

 nerve or some other portion of the apparatus. Hallucinations of 

 hearing are very common among the insane. 



How is the voice produced? 



The vibration of the vocal cords is produced by the passage of 

 the air in expiration, never naturally in inspiration. The quality 

 of the voice as regards pitch depends upon the length of the vocal 

 cords, the crico-thyroid muscles acting to increase the tension, 

 while the thyro-arytenoid relax the cords and the crico-arytenoids 

 dilate and contract the rima glottidis. Falsetto and high-pitched 

 notes in a naturally low-pitched voice are due to vibration at the 

 edges of the cords. The hollow spaces about the oral and nasal 

 cavities are of use as resonators or sounding-boards. 



What organs are used in the formation of articulate speech ? 



The tongue and teeth in the formation of the linguals and den- 

 tals, the nasal sounds by the cavity of the nose ; the other sounds 

 are formed largely by modifications in the shape of the mouth in 

 one or another part. 



What range has the human voice in respect of pitch ? 



From one to three octaves : in this cultivation and natural apti- 

 tude are factors which permit great variability. The total range 

 of the human voice from the highest soprano to the lowest bass is 

 about four octaves. Thus it will be seen that the range of sounds 

 which can be appreciated by the ear is far beyond the capacity of 

 the voice. 



SIGHT. 



What is the function of the eye ? 



The reception of stimuli of light, whereby we are able to per- 

 ceive the impressions of form, color, and conditions of our sur- 

 roundings in infinite variety. It is far the most complex in 

 structure of any of the organs of special sense, and the most rapid 

 and delicate in its actions. 



