DIGESTION IN THE MOUTH. 285 



when mastication is rapid, and is therefore greatest at the beginning of 

 a meal, unless after a very prolonged fast, when a certain amount of 

 time seems to be required b} r the glands to reach their maximum activity. 

 The submaxillary glands secrete together, and each give about the same 

 quantity of saliva, although this amount is not one-third of that secreted 

 by the parotid, even in animals in which these glands appear to be of 

 about the same size. The Unguals also secrete together, and the same 

 may be assumed of the molars and other glands. These characters may 

 be determined by making fistulse of the different excretory ducts of the 

 glands, and so conveying certain portions of the saliva out of the mouth 

 and then weighing the increase of weight in the food in its passage 

 through the mouth to a fistulous opening in the oesophagus. During 

 rumination the parotids have been found by this method, as well as by 

 the production of parotid fistulse, to pour out a large quantity of fluid, 

 even although the food lias been already comminuted and thoroughly 

 moistened in the first mastication and during its sojourn in the rumen. 

 The quantity of saliva is very little less than that poured out by the first 

 mastication, and here also the parotids preserve their alternate, intermit- 

 tent action ; but the food does not pass between the incisor teeth in the 

 second mastication, so these teeth are inactive, and the anterior salivary 

 system remains almost quiescent. Though thej 7 continue to secrete, they 

 do not give any more fluid during this time than during abstinence. 

 This is a peculiarity of the salivary secretion during rumination, and 

 shows the relative independence of the different glands. Duringabstinence 

 new features are met with, which vary in different animals. In the fast- 

 ing horse the parotids are inactive, and the submaxillaries give only a 

 few drops of fluid, but the mouth is always moist, and the horse will 

 often be seen to swallow the fluids which collect in the month, even after 

 fistulse have been made for both parotids and both submaxillary glands. 

 Hence, by exclusion, the fluid must have come from the Unguals, tonsils, 

 and palatine glands. In the fasting ruminants the parotids are not in- 

 active. They pour into the mouth during abstinence about one-eighth or 

 one fourth as much as they secrete during mastication. Here, also, the 

 submaxillaries secrete little fluid, but the sublinguals, superior molars, 

 and palatine glands, judging by the viscidity of the fluid, must be more 

 or less active. This continued salivary secretion in the ruminant we will 

 find later to be of great importance in aiding the function of rumination. 

 Finally, when stimulated by sapid substances we find marked differences 

 in the response of different glands to these stimuli. The parotids are 

 not sensibly affected, and the glands, which furnish a viscid saliva, are all 

 more or less stimulated, according to the chemical character and intensity 

 of the excitation, and the extent of surface to which it is applied, and 

 its duration. 



