CHAPTER III 

 SALIVARY DIGESTION 



THE saliva is secreted by three pairs of glands, the submaxillary, 

 sublingual, and parotid, reinforced by numerous small glands called 

 buccal glands. The saliva secreted by each pair of glands possesses 

 certain definite characteristics peculiar to itself. For instance, in man 

 the parotid glands ordinarily secrete a thin, watery fluid, the submaxil- 

 lary glands secrete a somewhat thicker fluid containing mucin, while the 

 product of the sublingual glands has a more mucilaginous character. 

 The saliva as collected from the mouth is the combined product of all 

 the glands mentioned. The fact that there are pronounced variations 

 in the composition of different fractions of saliva secreted by the same 

 normal individual on a uniform diet has been emphasized by Lothrop 

 and Gies. 1 



The saliva may be induced to flow by many forms of stimuli, such as 

 chemical, mechanical, electrical, thermal, and psychical, the nature and 

 amount of the secretion depending, to a limited degree, upon the par- 

 ticular class of stimuli employed as well as upon the character of the 

 individual stimulus. For example, in experiments upon dogs it has been 

 found that the mechanical stimulus afforded by dropping several pebbles 

 into the animaPs mouth caused the flow of but one or two drops of 

 saliva, whereas the mechanical stimulus afforded by sand thrown into 

 the mouth induced a copious flow of thin watery fluid. Again, when 

 ice-water or snow was placed in the animal's mouth no saliva was seen, 

 while an acid or anything possessing a bitter taste, which the dog wished 

 to reject, caused a free flow of the thin saliva. On the other hand, when 

 articles of food were placed in the dog's mouth the animal secreted a 

 thicker saliva having a higher mucin content a fluid which would lubri- 

 cate the food and assist in the passage of the bolus through the esopha- 

 gus. It was further found that by simply drawing the attention of the 

 animal to any of the substances named above, results were obtained 

 similar to those secured when the substances were actually placed in the 

 animaPs mouth. For example, when a pretense was made of throw- 

 ing sand into the dog's mouth, a watery saliva was secreted, whereas 

 food under the same conditions excited a thicker and more slimy 

 secretion. The exhibition of dry food, in which the dog had no par- 



1 Lothrop and Gies: Journal of the Allied (Dental] Societies, 6, 65, .1911. 



54 



