LESSON 59.1 THE SALIVARY GLANDS. 207 



ducts of the parotid glands are situated, as we have seen, in immedi- 

 ate proximity to the molar teeth, and the secretion is only evolved 

 by their action ; the probability is that the incisor teeth, used in bit- 

 ing, and the interior of the mouth, are usually lubricated by the se- 

 cretion of one or both of the other pairs of glands, whilst the parotid 

 glands are reserved for mastication alone. 



895. Whatever light chemistry may throw upon this really im- 

 portant question, remains to be seen, but Comparative Anatomy, the 

 only sure guide in the settlement of abstruse and difficult subjects 

 of this kind, would appear to settle it conclusively, that the secre- 

 tion of the parotid glands affects solely the vitality of all tissues 

 presented to their action ; and the secretion of the other glands has 

 the power of rapidly decomposing or disintegrating tissues already 



896. The third function of the saliva is no less important, name- 

 ly, to dilute or moisten dry food, and is common to all these glands. 



The blood of man and animals is too rich and thick to be con- 

 sumed in its natural state by parasitic insects ; and the motive they 

 have for pouring their secretion liberally into the wound they have 

 made, is twofold, one to destroy the vitality of the blood, a func- 

 tion their stomach cannot perform, and the other to dilute it, to 

 make it thin enough to be pumped up with ease. 



897. In insects, the anatomical position of their salivary glands 

 does not appear to warrant the opinion that they, at least, possess 

 parotid glands ; but the life-destroying character of the salivary se- 

 cretion in all the predaceous, carnivorous, and parasitic tribes, in ad- 

 dition to the same exhibition in all those insects feeding upon living 

 vegetable matter, too clearly points to the function and character of 

 the parotid secretion, notwithstanding the situation of their glands. 



898. And why should it be necessary for such insects to have 

 two, and frequently three pairs of such glands, if they all possessed 

 the same capabilities ? From this circumstance alone, it would ap- 

 pear that the function is divided ; that one pair of these glands has 

 the power of destroying life, and the other pair (or pairs) of decom- 

 posing organic matter already dead both these processes being essen- 

 tial to the ultimate digestion of the food. 



899. In the Nepa (water Scorpion), there are three pairs of sali- 

 vary glands three of them lying on the right and three on the left 

 side of the body. One pair of these glands possesses a distinct outlet, 

 and from the effects it produces by inoculation, entomologists have 

 long ago concluded that these especial glands secrete a poisonous 



