728 SPECIAL SENSES. 



yond the analysis made many years ago by Frerichs. According to this 

 observer the following is the composition of the lachrymal secretion : 



COMPOSITION OF THE TEARS. 



Water 990-GO to 987-00 



Epithelium 1'40 " 3-20 



Albumen 0-80 " 1-00 



Sodium chloride. ....") 

 Alkaline phosphates. I 



Earthy phosphates.. V 7-20 " 8'80 



Mucus | 



Fat J 



1,000-00 1,000-00 



The specific gravity of the tears has never been ascertained. The liquid 

 is perfectly clear, colorless, of a saltish taste and a feebly alkaline reaction. 

 The albumen given in the table is called by some authors, lachrymine, thrae- 

 nine or dacryoline. This substance, whatever it may be called, resembles 

 mucus in many regards and probably is secreted by the conjunctiva and not 

 by the lachrymal glands. Unlike ordinary mucus, it is coagulated by water. 



The secretion of tears is readily influenced through the nervous system. 

 Aside from the increased flow of this secretion from emotional causes, which 

 probably operate through the sympathetic, a hypersecretion almost imme- 

 diately follows irritation of the mucous membrane of the conjunctiva or of 

 the nose. The same result follows violent muscular effort, laughing, cough- 

 ing, sneezing etc. The secretion of tears following stimulation of the mu- 

 cous membrane is reflex. 



CHAPTEE XXIII. 



A UDITION. 



Anditory (eighth nerve) General properties of the auditory nerves Topographical anatomy of the parts 

 essential to the appreciation of sound The external ear General arrangement of the parts composing 

 the middle ear Anatomy of the tympanum Arrangement of the ossicles of the ear Muscles of the 

 middle ear Mastoid cells Eustachian tube Muscles of the Eustachian tube General arrangement of 

 the bony labyrinth Physics of sound Noise and musical sounds Pitch of musical sounds Musical 

 scale Quality of musical sounds Harmonics, or overtones Resultant tones Summation tones Har- 

 mony Discords Tones by influence Uses of different parts of the auditory apparatus Structure of the 

 membrana tympani Uses of the membrana tympani Mechanism of the ossicles of the ear Physiologi- 

 cal anatomy of the internal ear General arrangement of the membranous labyrinth Liquids of the 

 labyrinth Distribution of nerves in the labyrinth Organ of Corti Uses of different parts of the inter- 

 nal ear Centres for audition. 



IMPRESSIONS of sound are conveyed to the brain by special nerves; but 

 in order that these impressions shall reach these nerves so as to be properly 

 appreciated, a complex accessory apparatus is required, the integrity of which 

 is essential to perfect audition. The study of the arrangement and action 

 of these accessory parts is even more important and is far more intricate than 



