648 THE SENSES 



Most of the substances taken as foods into the mouth give off odorous 

 particles that stimulate the olfactory membrane. In fact, the chief elements 

 in food flavors are not tastes, but smells, or combinations of the two. This 

 is particularly true of meats. Meats are especially prized for their delicate 

 flavors, and cooking is performed to bring out these flavors. Yet meat has 

 little taste other than salt; the so-called tastes are due to odorous particles 

 entering the nostril and stimulating the olfactory membrane at the same 

 moment the taste buds of the mouth are stimulated. 



Subjective sensations occur frequently in connection with the sense of 

 smell. Often a person smells something which is not present, and which 

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

 it occasionally happens to every one. In a man who was conscious of a bad 

 odor, the arachnoid was found after death to be beset with deposits of bone, 

 and a lesion in the middle of the cerebral hemispheres was also discovered. 

 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. 



III. HEARING AND EQUILIBRATION. 

 THE ANATOMY OF THE EAR. 



For descriptive purposes, the ear, or organ of hearing, is divided into 

 three parts, i, the external, 2, the middle, and 3, the internal ear. The first 

 two are only accessory structures to the third, which contains the essential 

 parts of the organ of hearing. The accompanying figure, 430, shows very 

 well the relation of these divisions to each other. 



The External Ear. The external ear consists of the pinna or auricle 

 and the external auditory canal or meatus. 



The principal parts of the pinna, figure 430, are two prominent rims en- 

 closed one within the other, the helix and antihelix, and inclosing 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 anti- 

 tragus. From the concha, the auditory canal passes inward and a little 

 forward to the membrana tympani, to which it thus serves to convey the 

 vibrations of the air. It consists of a fibro-cartilage tube lined by skin con- 

 tinuous with that of the pinna, and extending over the outer part of the mem- 

 brana tympani. Fine hairs and sebaceous glands are present toward the 

 outer part of the canal, while deeper in the canal are small glands, resembling 

 the sweat glands in structure, which secrete the cerumen. 



Regarding the external ear, therefore, as a collector and conductor of 

 sonorous vibrations, all its inequalities, elevations, and depressions become 

 of evident importance; for those elevations and depressions upon which the 

 undulations fall will tend to intensify certain sound waves while not affecting 



