DIGESTION 341 



alone causes neither secretion nor atrophy, nor does removal of the 

 superior cervical ganglion. The histological characters of the gland- 

 cells during paralytic secretion are those of { rest.' 



Reflex Secretion of Saliva. The reflex mechanism of 

 salivary secretion is very mobile, and easily set in action by 

 physical and mental influences. It is excited normally by 

 impulses which arise in the mouth, especially by the contact 

 of food with the buccal mucous membrane and the gustatory 

 nerve-endings. The mere mechanical movement of the 

 jaws, even when there is nothing between the teeth, or only 

 a bit of a non-sapid substance like indiarubber, causes 

 secretion. The vapour of glacial acetic acid or ether gives 

 rise to a rush of saliva, as does gargling the mouth with 

 distilled water. The smell, sight, or thought of food, and 

 even the thought of saliva itself, may act on the salivary 

 centre through its connections with the cerebrum, and make 

 ' the teeth water.' A copious flow of saliva, reflexly excited 

 through the gastric branches of the vagus, is a common 

 precursor of vomiting ; the introduction of food into the 

 stomach also excites salivary secretion. 



In most animals and in man the activity of the large 

 salivary glands is strictly intermittent. But the smaller glands 

 that stud the mucous membrane of the mouth never entirely 

 cease to secrete, and the same is the case with the parotid 

 in ruminant animals. 



The centre is situated in the medulla oblongata, stimula- 

 tion of which causes a flow of saliva. The chief afferent 

 paths to the salivary centre are the lingual branch of the 

 fifth and the glosso-pharyngeal ; but stimulation of many 

 other nerves may cause reflex secretion of saliva. In ex- 

 perimental stimulation, the sole efferent channel seems to 

 be the cerebral nerve-supply of the glands. After section 

 of the chorda, no reflex secretion by the submaxillary gland 

 can be caused, although the sympathetic remains intact. 



It was alleged by Bernard that, after division of the 

 chordo-lingual, a reflex secretion could be obtained from the 

 submaxillary gland by stimulating the central end of the 

 cut lingual nerve between the so-called submaxillary ganglion 

 and the tongue, the ganglion being supposed to act as 



