156 DIGESTION. 



which may be collected at any time in small quantity by the 

 simple act of sputation, is composed of the secretions of a 

 considerable number and variety of glands. The most im- 

 portant of these are the parotid, submaxillary, and sublin- 

 gual, which are usually called the salivary glands, and, in 

 addition, the labial and buccal glands, the follicular glands of 

 the tongue and general mucous surface, and certain glandular 

 structures in the mucous membrane of the pharynx. The 

 liquid which becomes more or less incorporated with the food 

 before it descends to the stomach, and which must be con- 

 sidered as the digestive fluid of the mouth, is known as the 

 mixed saliva ; but the study of the composition and proper- 

 ties of this fluid as a whole should be prefaced by a consid- 

 eration of the different fluids of which it is composed. 



The salivary glands belong to the variety of glands called 

 racemose. They closely resemble the other glands belonging 

 to this class, and their structure will be considered more par- 

 ticularly under the head of secretion. 



Parotid Saliva. The parotid is the largest of the three 

 salivary glands. It is situated below and in front of the ear, 

 and opens, by the duct of Steno, into the mouth at about the 

 middle of the cheek. The papilla which marks the orifice 

 of the duct is situated opposite the second large molar tooth 

 of the upper jaw. Bernard, to whom belongs the credit of 

 having established the general physiological distinctions be- 

 tween the different fluids which enter into the composition 

 of the mixed saliva, cites Hapel de la Chenaie as the first to 

 obtain the pure parotid saliva from the horse, by section of 

 the duct of Steno, in 1780. 1 Tiedemann and Gmelin, in their 

 work on digestion, recognized the distinction between the 

 saliva found in the mouth, and the secretion of the parotid, 



1 BERNARD, Lemons de Physiologie Experimentale, Paris, 1856, p. 30. The 

 original memoir by Hapel de la Chenaie ( Observations et Experiences sur V analyse 

 de la Salive du ChevaT), is published in the Memoires de la Societe Royale de Me- 

 decine, Paris, 1780 and 1781, p. 325. 



