THE SALIVA. 145 



sulphocyanide which may be detected, as we have seen, after the organic 

 matters have been precipitated by alcohol. 



Both the parotid saliva and that from the submaxillary gland in the 

 human subject contain ptyaline, but they differ considerably, as in the 

 case of the lower animals, in their degree of viscidity. 



Mode of Secretion of the Saliva. The different salivary glands vary 

 in the quantity of fluid secreted by them and in the different influences 

 which excite them to activity. As shown by Bernard, the parotid 

 saliva is most abundantly poured out under the stimulus of anything 

 which excites the movement of the jaws, as in the mastication of dry 

 substances, or continuous speaking ; while that of the submaxillary is 

 especially increased by the introduction of substances which excite the I 

 sense of taste. According to the same experiments, the secretion of the 

 sublingual glands in the dog is particularly excited at the moment of 

 deglutition, and aids, together with that of the muciparous glandules, in 

 lubricating the surface of the mouth and fauces, and in facilitating the 

 passage of the masticated food through the oesophagus. Colin, in expe- 

 rimenting upon the horse and the ox, 1 found also that the parotid saliva 

 in these animals is abundantly excited by the movements of mastication, 

 but not by the simple contact of sapid substances with the mucous mem- 

 brane of the mouth ; while, on the other hand, the secretion of the sub- 

 maxillary saliva is considerably increased by introduction into the mouth 

 of substances having a marked taste. Both the parotid and submaxillary 

 secretions are abundant while the animal is feeding, their quantity being 

 proportional to the rapidity of mastication and the sapid quality of the 

 alimentary substances. They are both either suspended or very much 

 diminished during abstinence. In the ruminants, however, the sublingual 

 saliva, like the submaxillary, is excited by sapid substances ; it is also 

 secreted continuously while the animal is feeding, and not simply at the 

 moment of deglutition. It continues to be secreted during abstinence, 

 and contributes to the supply of fluid by which the surfaces are kept in 

 a moist condition. 



Another fact observed by Colin which indicates the different nervous 

 influences by which the salivary glands are controlled, is that in the 

 ruminant animals while feeding both the parotid and submaxillary 

 glands furnish an abundant supply of saliva ; but during the process of 

 rumination, although the parotid glands are in full secretion, discharging 

 frequently as much as 900 grammes of saliva in a quarter of an hour, 

 the submaxillary glands are entirely inactive or produce only an insig- 

 nificant quantity of fluid. Colin has also found that in the horse and ass, 

 as well as in the ox and other ruminating animals, the parotid glands of 

 the two opposite sides, during mastication, are never in active secretion 

 at the same time; but that they alternate with each other, one remain- 

 ing quiescent while the other is active, and vice versa. In these animals 

 mastication is said to be unilateral, that is, when the animal commences 



Physiologie compare des Animaux Domestiques. Paris, 1854, tome i. p. 468. 



