710 SPECIAL SENSES 



Little is known in regard to the chemical composition of tears 

 beyond an analysis made many years ago by French s. According to 

 this observer, the following is the composition of the lachrymal secre- 

 tion : 



COMPOSITION OF THE TEARS 



Water . . 990.60 to 987.00 



Epithelium r-.4o to 3.20 



Albumin 0.80 to i.oo 



Sodium chloride 1 



Alkaline phosphates I 



Earthy phosphates } . . . . 7.20 to 8.80 



Mucus 



Fat 



1000.00 1000.00 



The specific gravity of the tears has not been ascertained. The 

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

 The albumin given in the table is called by some authors, lachrymin, 

 thraenin or dacryolin. 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. It is supposed to be a globulin (Halliburton). 



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 hypersecre- 

 tion almost immediately follows irritation of the mucous membrane of 

 the conjunctiva or of the nose. The same result follows violent mus- 

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

 following stimulation of the mucous membrane is reflex. 



