284 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



by an opening in the oesophagus. Such fluids, of course, are composed 

 of the sublingual saliva, together with the secretion of the buccal glands. 

 The sublingual saliva, obtained in man by the introduction of a fine 

 cannula, is secreted in isolated, clear, very viscid, alkaline drops ; hardly 

 enough, however, has been collected to determine its properties. In ani- 

 mals it is very transparent, thick, and so viscid as scarcely to deserve the 

 name of a liquid, and when a cannula is inserted in the duct it flows from 

 the orifice in a continuous thread. It contains 2.15 per cent, of solids, 

 according to Heidenhain, while according to Kiihne the proportion may 

 rise to 9.98 pur cent. Mucin and sulphocyanide of potassium have been 

 detected in it. It apparently contains no bicarbonate of sodium, as it 

 does not effervesce when acids are added to it. The sublingual secretion 

 is constant, though it is augmented greatly during feeding, and the prin- 

 cipal stimuli which call it forth are those which pass through the sense 

 of taste. 



In addition to the above secretions, fluid is also poured into the 

 mouth by the various buccal glands. Its characters can only be studied 

 by ligating all the salivary ducts. When this is accomplished in the dog 

 the mucous membrane in the mouth only remains moist as long as the 

 mouth is closed. Dry food is then only with the greatest difficulty mas- 

 ticated and swallowed, and the thirst of such animals is consequently 

 greatly increased. It follows from this that the secretion of the mucous 

 glands of the mouth must be very slight, and, in fact, only one or two 

 grammes may be collected with the greatest care in an hour. It has an 

 alkaline reaction, and has been determined by Bidder and Schmidt to 

 contain 9.98 per cent, of solids. Attempts have been made to study the 

 properties of the secretions of the buccal glands by making aqueous 

 infusions of these glands after death. The superior molar glands, which 

 have been termed the accessory parotids in the ox, give a viscid extract 

 with water, while such an extract of the inferior molars is much less 

 viscid. Very little has been determined as to the properties of these 

 'secretions. 



4. General Characteristics of the Salivary Secretion.— Although it 

 has been seen that each gland differs somewhat in its manner of secreting 

 and in the results of that process, nevertheless, the general salivary sys- 

 tem has certain distinguishing characteristics, which have been carefully 

 studied by Colin, according to the principal conditions in which ani- 

 mals may happen to be ; thus, the conditions may vary, according as 

 the animal is feeding, ruminating, fasting, or whether stimulating sub- 

 stances are in contact with the mucous membrane of the mouth. Dur- 

 ing feeding two of the glands secrete actively, though unequally ; as 

 has been seen, the parotid on the side of mastication gives double or 

 treble as much saliva as the opposite gland. The amount is also greater 



