LACHRYMAL APPARATUS. 



Composition of the Tears. 1 



Water 990'60 to 987*00 



Epithelium 1'40 " 3'20 



Albumen 0'80 " 1-00 



Chloride of sodium, "j 

 Alkaline phosphates, 



Earthy phosphates, I 7'20- " 8'80 



Mucus, 



Fat, J 



1000-00 1000-00 



The specific gravity of the tears has never been ascer- 

 tained. 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, thrsenine, or 

 dacryoline. 8 This substance, whatever it may be called, re- 

 sembles mucus in many regards, and is probably secreted by 

 the conjunctiva and not by the lachrymal glands. It differs 

 from ordinary mucus in being coagulated by water. 3 



The secretion of tears is readily influenced through the 

 nervous system. Aside from the increased flow of this secre- 

 tion from emotional causes, which probably operate through 

 the sympathetic, a hypersecretion almost immediately follows 

 irritation of the mucous membrane of the conjunctiva or of 

 the nose. The same result follows violent muscular effort, 

 laughing, coughing, sneezing, etc. The secretion of tears 

 under stimulation of the mucous membrane is reflex. A 

 number of years ago, Magendie transfixed with a needle 

 the lachrymal nerve in a man, and passed through it a feeble 

 galvanic current, producing an excessive flow of tears. 4 The 

 action in this case was undoubtedly reflex. 



1 FRERICHS, Thranensecrdion, in WAGNER, Handioorterbuch der Physiologic, 

 Braunschweig, 1846, Bd. Hi., Erste Abtheilung, S. 618. 



2 ROBIN ET VERDEIL, Chimie anatomique, Paris, 1853, tome iii., p. 452. 



3 See vol. iii., Secretion, p. 56. 



4 MAGEXDIE, Precis elementaire de physiologic, Paris, 1836, tome i., p. 59, 

 note. 



