THE SENSES. 179 



persons; for as some have no ear for music (as it is said), so others have 

 no clear appreciation of the relation of odors, and therefore little pleasure 

 in them. 



Subjective Sensations of Smell. The sensations of the olfactory 

 nerves, independent of the external application of odorous substances, 

 have hitherto been little studied. The friction of the electric machine 

 produces a smell like that of phosphorus. Ritter, too, has observed, that 

 when galvanism is applied to the organ of smell, besides the impulse to 

 sneeze, and the tickling sensation excited in the filaments of the fifth 

 nerve, a smell like that of ammonia was excited by the negative pole, and 

 an acid odor by the positive pole; whichever of these sensations were 

 produced, it remained constant as long as the circle was closed, and 

 changed to the other at the moment of the circle being opened. Subjec- 

 tive sensations occur frequently in connection with the sense of smell. 

 Frequently a person smells something which is not present, and which 

 other persons cannot smell; this is very frequent with nervous people, but 

 it occasionally happens to every one. In a man who was constantly con- 

 scious of a bad odor, the arachnoid was found after death to be beset 

 with deposits of bone; and in the middle of the cerebral hemispheres were 

 scrofulous cysts in a state of suppuration. Dubois was acquainted with a 

 man who, ever after a fall from his horse, which occurred several years 

 before his death, believed that he smelt a bad odor. 



HEARING. 



Anatomy of the Ear. For descriptive purposes, the Ear, or Organ 

 of Hearing, is divided into three parts, (1) the external, (2) the middle, 

 and (3) the internal ear. The two first are only accessory to the third or 

 internal ear, which contains the essential parts of an organ of hearing. 

 The accompanying figure shows very well the relation of these divisions, 

 one to the other (Fig. 357). 



(1.) External Ear. The external ear consists of the pinna or auricle, 

 and the external auditory canal or meatus. 



The principal parts of the pinna (Fig. 358, A) are two prominent rims 

 enclosed one within the other (Helix and antilielix), and enclosing a central 

 hollow named the concha; in front of the concha, a prominence directed 

 backward, the tragus, and opposite to this, one directed forward, the 

 antitragus. From the concha, the auditory canal, with a slight arch di- 

 rected upward, passes inward and a little forward to the membrana tym- 

 pani, to which it thus serves to convey the vibrating air. Its outer part 

 consists of fibro-cartilage continued from the concha; its inner part of 

 bone. Both are lined by skin continuous with that of the pinna, and 

 extending over the outer part of the membrana tympani. 



Toward the outer part of the canal are fine hairs and sebaceous glands, 

 while deeper in the canal are small glands, resembling the sweat-glands 



