CHEMISTRY OF MAN. 



CHAPTER III. 



THE SECRETIONS OF THE CHYLOPOIETIC VISCERA, AND THE 

 THEORY OF DIGESTION. 



The Saliva. 



THE saliva is a peculiar fluid, secreted by the parotid, sub- 

 maxillary, and sublingual glands, and conveyed from them by 

 certain ducts into the cavity of the mouth, where it becomes 

 mixed with the buccal mucus. It may, however, be obtained 

 in a state of purity by collecting it as it flows from one of the 

 ducts. The following observations respecting the secretion 

 of the saliva were made by Mitscheriich, 1 on a person with a 

 salivary fistula, in whom the saliva could be collected directly 

 from Steno's duct. He found that there was no flow of saliva 

 while the muscles of mastication and of the tongue were in a 

 state of perfect repose, and all nervous excitement avoided. 

 He likewise observed that, during the acts of eating and drink- 

 ing, (especially at the commencement,) the secretion was 

 abundant, being proportionate to the stimulating nature of the 

 food and to the degree it was masticated. From two to three 

 ounces of saliva were collected from one of the parotid glands 

 in the course of twenty-four hours. It is usually supposed that 

 about ten or twelve ounces of saliva are secreted daily, but accu- 

 rate observations are still required on this subject. 



Human saliva is a rather opalescent, viscid, colourless fluid ; 



1 Rust's Magaz. vol. 40. 

 II. 1 



