546 THE SENSE OF HEARING. 



accommodated to distance, nor to the perception of the particu- 

 lar part of the nerve affected ; but just as one person sees dis- 

 tinctly only in a bright light, and another only in a moderate 

 light, so in different individuals the sense of hearing is more 

 perfect for sounds of different pitch ; and just as a person 

 whose vision for the forms of objects, &c., is acute, neverthe- 

 less distinguishes colors with difficulty, and has no perception 

 of the harmony and disharmony of colors, so one, whose hear- 

 ing is good as far as regards the sensibility to feeble sounds, is 

 sometimes deficient in the power of recognizing the musical 

 relation of sounds, and in the sense of harmony and discord ; 

 while another individual, whose hearing is in other respects 

 imperfect, has these endowments. The causes of these differ- 

 ences are unknown. 



Subjective sounds are the result of a state of irritaton or 

 excitement of the auditory nerve produced by other causes 

 than sonorous impulses. A state of excitement of this nerve, 

 however induced, gives rise to the sensation of sound. Hence 

 the ringing and buzzing in the ears heard by persons of irrita- 

 ble and exhausted nervous system, and by patients with cerebral 

 disease, or disease of the auditory nerve itself; hence also the 

 noise in the ears heard for some time after a long journey in a 

 rattling noisy vehicle. Hitter found that electricity also excites 

 a sound in the ears. From the above truly subjective sound 

 we must distinguish those dependent, not on a state of the audi- 

 tory nerve itself merely, but on sonorous vibrations excited in 

 the auditory apparatus. Such are the buzzing sounds atten- 

 dant on vascular congestion of the head and ear, or on aneu- 

 rismal dilatation of the vessels. Frequently even the simple 

 pulsatory circulation of the blood in the ear is heard. To the 

 sounds of this class belong also the snapping sound in the ear 

 produced by a voluntary effort, and the buzz or hum heard 

 during the contraction of the palatine muscles in the act of 

 yawning ; during the forcing of air into the tympanum, so as 

 to make tense the membrana tympani ; and in the act of blow- 

 ing the nose, as well as during the forcible depression of the 

 lower jaw. 



Irritation or excitement of the auditory nerve is capable of 

 giving rise to movements in the body, and to sensations in 

 other organs of sense. In both cases it is probable that the 

 laws of reflex action, through the medium of the brain, come 

 into play. An intense and sudden noise excites, in every 

 person, closure of the eyelids, and, in nervous individuals, a 

 start of the whole body or an unpleasant sensation, like that 

 produced by an electric shock, throughout the body, and 

 sometimes a particular feeling in the external ear. Various 



