208 DIGESTION. 



is chiefly, although not exclusively, connected with mastication and indirectly, with deglu- 

 tition ; for it is only by becoming incorporated with this saliva, that the deglutition of 

 dry, pulverulent substances is rendered possible. Facts in comparative physiology, show- 

 ing a great development of the parotids in animals that masticate very thoroughly, par- 

 ticularly the ruminants, a slight development in those that masticate but slightly, and the 

 absence of these glands in animals that do not masticate at all, are additional arguments 

 in favor of these views. 



Submaxillary Saliva. In the human subject, the submaxillary is the second of the 

 salivary glands in point of size. Its minute structure is the same as that of the parotid. 

 As its name implies, it is situated below the inferior maxillary bone. It is in the anterior 

 part of what is known as the submaxillary triangle of the neck. Its excretory duct, called 

 sometimes the duct of Wharton, is about two inches in length and passes from the 

 gland, beneath the tongue, to open by a small papilla by the side of the frenum. This 

 gland is relatively very small in the herbivora but is largely developed in the carnivora, 

 in the latter being larger than the parotid. 



The pure submaxillary saliva presents many important points of difference from the 

 secretion of the parotid. It was first studied as a distinct fluid by Bernard. It may be 

 obtained by exposing the duct and introducing a fine silver tube, when, on the introduc- 

 tion of any sapid substance into the mouth, the secretion will flow in large, pearly drops. 

 Bernard found this variety of saliva much more viscid than the parotid secretion. It is 

 perfectly clear, and, on cooling, frequently becomes of a gelatinous consistence. Its 

 organic matter is not coagulable by heat. In the dog, it is rather more strongly alkaline 

 than the parotid saliva. According to Bernard, it does not contain the sulpho-cyanide 

 of potassium. 



The submaxillary gland pours out its secretion in greatest abundance when sapid sub- 

 stances are introduced into the mouth. In the solipeds and ruminants, Colin has ob- 

 served that the quantity of submaxillary saliva secreted is much increased during eating; 

 but, unlike the parotids, the secretion does not alternate on the two sides with the alter- 

 nation in mastication. He has found, in all the domestic animals, that the flow is greatly 

 influenced by the degree of sapidity of the food. Although sapid articles induce an 

 abundant secretion from the submaxillary glands, they also produce an increase in the 

 secretions from the parotids and sublinguals ; and, on the other hand, movements of 

 mastication increase somewhat the flow from the submaxillaries, and these glands secrete 

 a certain amount of fluid during the intervals of digestion. The viscid consistence of the 

 submaxillary saliva renders it less capable of penetrating the alimentary mass during 

 mastication than the parotid secretion, so that it remains chiefly near the surface of the 

 alimentary mass. 



Sullingual Saliva. The sublinguals, the smallest of the salivary glands, are situated 

 beneath the tongue, on either side of the frenum. In minute structure they resemble the 

 parotid and the submaxillary glands. Each gland has a number of excretory ducts, from 

 eight to twenty, which open into the mouth by the side of the frenum ; and one of the 

 ducts, larger than the others, joins the duct of the submaxillary gland near its termina- 

 tion in the mouth. 



The secretion of the sublingual glands is more viscid even than the submaxillary sali- 

 va, but it differs in the fact that it does not gelatinize on cooling. It is so glutinous that 

 it adheres strongly to any vessel and flows with difficulty from a tube introduced into 

 the duct. Like the secretion from the other salivary glands, its reaction is distinctly al- 

 kaline. Its organic matter is not coagulable by heat, acids, or the metallic salts. Ac- 

 cording to Bernard, after desiccation it is redissolved by water and its viscid properties 

 are then restored. 



In accordance with the view entertained by Bernard concerning the function of this 



