SALIVARY GLANDS. 



429 



would be situated between the cheek and the 

 teeth, the quantity of saliva amassed in the 

 canal of the duct, by its temporary oblitera- 

 tion, would flow down and become intimately 

 mixed up with the particles of the food, which 

 would now entirely surround its orifice. This 

 relation, then, of the buccinator with the 

 duct of the parotid would seem to regulate 

 the supply of saliva, which, if this view be 

 correct, flows down only at a time when it 

 can be most thoroughly incorporated with the 

 material during its mastication. The relation 

 of the ducts of the submaxillary and subiingual 

 glands to this process would seem to be of far 

 less importance. The orifices of Wharton's 

 ducts and the sublingual ducts situated behind 

 the incisor teeth, would appear to hold a 

 direct relation only to the primary stage of 

 mastication, that is to say, lubricating with the 

 saliva the larger masses into which the food 

 is broken up during that process, and probably 

 after its completion, immediately prior to the 

 passage of the whole mass into the stomach. 



The position, then, of the duct of the 

 parotid, which is so situated that mechanical 

 means are brought into play, in order to 

 insure the thorough incorporation of its saliva 

 with the food, and the great comparative size 

 of the gland itself, lead naturally to the in- 

 ference that the parotid is by far the most 

 important gland in the series, the submaxillary 

 and lingual having but a subordinate function. 

 This deduction has been experimentally proved 

 by Bernard*, who, having made an aperture 

 at the lower part of the oesophagus of a 

 horse, administered to the animal about sixteen 

 ounces of oats. Fifteen or sixteen seconds 

 after the commencement of mastication, a 

 rounded mass made its appearance at the 

 cesophageal opening, well triturated, perfectly 

 moist, pasty in the interior, and covered on 

 the exterior by a moderately thick layer of 

 tenacious mucus and saliva. A fresh quantity 

 of the oats, in a similar condition, was pro- 

 jected every three-quarters of a minute. At 

 the end of nine minutes, the mastication of 

 the entire quantity having been finished, the 

 ducts of the parotid were divided, so that the 

 saliva that was secreted could be conducted 

 out of the mouth. The same quantity of 

 oats was again given to the animal. In this 

 second experiment mastication did not appear 

 to be attended with any particular incon- 

 venience, and was performed as easily as in 

 the first. It was exerted, however, a much 

 longer time ; for a minute and a half elapsed 

 before the first mass made its appearance at 

 the opening : this, though well triturated, and 

 covered on its external surface with much 

 mucus, was considerably smaller than those 

 masses which had escaped from the cesopha- 

 gcal opening prior to the division of the ducts 

 of the parotid. The interior of the mass, 

 also, instead of being, like them, well mois- 

 tened and pasty, had but slight tenacity, and 



* Me'moires snr le Role de la Salive dans les Phe- 

 nomcnes de la Digestion. Archives Gene'rales de 

 Me'dicine, Janvier, 1817. 



was comparatively dry. Mastication and deglu- 

 tition now became more and more difficult, 

 lengthened, and laborious, so that an interval 

 of from two minutes and a half to three 

 minutes frequently occurred between the exit 

 from the oesophagus of the successive masses. 

 The horse, in its endeavours to swallow the 

 oats which appeared to adhere to the palate, 

 frequently gulped down a quantity of air, 

 which escaped with noise from the oesophagus 

 prior to the exit of the oats that had with 

 such difficulty passed into the canal. At the 

 end of twenty-five minutes, but little more 

 than eleven ounces of the oats had been mas- 

 ticated and swallowed, whereas, prior to the 

 division of the parotid ducts, sixteen ounces 

 had been well triturated and swallowed in 

 nine minutes. Bernard further remarks, that 

 he collected during the second experiment 

 the saliva that flowed from the parotid ducts, 

 and he found that it came away in an almost 

 continued current ; but that during the time 

 that he administered water to the animal not 

 a single drop of saliva escaped. The circum- 

 stance of the smallness of the masses passed 

 in the second experiment, and the dryness of 

 their interior, taken together with their ex- 

 terior envelope of tenacious mucus and saliva, 

 which was as abundant as before the division 

 of Steno's ducts, lead to the inference that the 

 former condition was owing to the absence 

 of the aqueous secretion of the parotid; the 

 latter condition, to the fact of the submaxillary 

 and sublingual glands being mainly engaged in 

 the secretion of a tenacious saliva. Further 

 experiments bring about the conclusion that 

 the fluid from the parotid on the one hand, 

 and from the submaxillary and sublingual on the 

 other, are regulated by conditions special to 

 each. Thus, the quantity of saliva secreted 

 by the parotid of a horse is in direct ratio to 

 the dryness of the food and the difficulty 

 experienced in its mechanical division. The 

 mastication of straw and hay causes the flow 

 of more than that of oats and farinaceous 

 matters; the mastication of moist forms of 

 food, hardly any. This, however, is by no 

 means the case with the saliva from" the 

 sublingual and the submaxillary ducts. This 

 always flows nearly in equal abundance 

 whether mastication be exerted on dry or 

 moist forms of food, and, owing to its com- 

 parative tenacity, is not easily imbibed into 

 the centre of the masticated material, but 

 gathers round the surface of the mass, thus 

 favouring its passage along the alimentary 

 canal. In a mechanical point of view, then, 

 there are two forms of saliva : the one clear 

 and aqueous, secreted from the parotid, and 

 which may be denominated the " saliva of 

 mastication" because its secretion is directly 

 related to this act ; the other tenacious and 

 secreted by the submaxillary and subliimual, 

 " the saliva of deglutition" because it always 

 lubricates the surface of the alimentary mass, 

 whether it be submitted to mastication or not. 

 The above views of Bernard are materially 

 strengthened by the fact of the high develop- 

 ment of the parotid in animals that masticate, 



