30 SALIVA. 



tion of saliva is only dependent on its nature, and as if, when fluid 

 or moist food is taken, the glands are not excited to activity. We 

 must, however, assume with Frerichs, that even in a state of per- 

 fect repose, the secretion of saliva is not totally suspended ; for 

 although Mitscherlich found scarcely a trace of saliva escaping 

 from the fistulous openings in the patients on whom he experi- 

 mented, when they had fasted for some time and were in a state of 

 perfect repose, and although we observe scarcely any secretion in 

 horses in whom a fistulous opening has been established, when 

 they have not been supplied with food for some time, we cannot sup- 

 pose that the process of secretion is absolutely suspended in these 

 any more than in other glands. Moreover we can form no opinion 

 regarding the normal secretion in a state of relative repose, from 

 the facts that during sleep, when the head is inclined forwards, and 

 in paralysis of the facial muscles, saliva is secreted in no sparing 

 quantity, since in both those cases the abundance of the secretion 

 is dependent on peculiar conditions. 



Physiologists have ever held the most varied opinions regard- 

 ing the physiological value of the saliva. We must, however, 

 regard the saliva as essentially fulfilling a threefold object of a 

 mechanical, a chemical, and a dynamical nature. 



The mechanical object is so manifest, that no one has ever 

 seriously doubted it ; for it is obvious to our senses, and requires 

 no demonstration to convince us that the moistening of dry food 

 in mastication serves, on the one hand, the better to adapt it for 

 deglutition, and, on the other hand, to separate the particles, and 

 thus allow them the more freely to be acted on by the other 

 digestive fluids. Formerly, however, the whole value of the 

 saliva was limited to this function ; and Bernard recently believed 

 that he had proved this view to be correct by the experiments to 

 which we have alluded. He maintained that the parotid saliva, by 

 its thin fluid property, serves to moisten the food, while the 

 tough and viscid secretion of the submaxillary glands affords a 

 mucous investment to the masticated food, lubricates it, and thus 

 adapts it for deglutition. 



W T e have already seen that the secretion of the submaxillary 

 glands is distinguished by its viscidity and toughness from the 

 parotid secretion, and even that infusions of these glands differ in 

 the same manner. In reference to this circumstance Bernard 

 notices the fact in comparative anatomy, that those animals which 

 swallow their food without masticating it, as, for instance, serpents, 

 birds, and reptiles, possess no parotid glands, or at most only 



