DIGESTION 109 



due to the rush of fluid which occurs when the bloodvessels are 

 dilated, or can the gland-cells expel their products in response 

 to nervous action ? In what way do the nerves of the gland 

 influence secretion ? Do they call for increased production, or 

 increased output, or both ? These are some of the problems 

 which the exposed situation of the submaxillary gland allows 

 physiologists to tackle. 



By means of a very simple operation, the ducts of one or both 

 parotid or submaxillary glands can be brought to the skin, 

 and made to pour their secretions on to the surface instead of 

 into the mouth. The flow under various circumstances can 

 be watched. The saliva can be collected and measured. 



The nerves of the submaxillary gland are easily isolated. A 

 nerve leaves the seventh (or facial), crosses the drum of the 

 ear, comes out through a minute crevice in the skull, and 

 runs for some little distance as a separate nerve before it 

 applies itself to the lingual branch of the fifth" which runs 

 along the side of the tongue. Owing to its passage across 

 the tympanic cavity (drum of the ear), it is termed " chorda 

 tympani." As its fibres are very small, they can be recognized 

 wherever they form a part of the lingual nerve. They leave 

 the lingual to go to a ganglion, the submaxillary ganglion, from 

 which the gland is supplied. The gland also receives branches 

 from the sympathetic nerve which ascends the neck. The last- 

 named branches accompany the facial artery. Stimulation of 

 either of these nerves causes the gland to secrete. The flow of 

 saliva which follows stimulation of the chorda tympani is much 

 more copious than that which follows stimulation of the sym- 

 pathetic, and as a rule it contains far less organic matter, 

 although about the same amount of mineral salts. Under 

 normal conditions the activity of the chorda tympani is 

 brought into play in a reflex manner by impulses which travel 

 up the nerves of taste (the lingual and glosso-pharyngeal) to 

 the cerebro-spinal axis ; but almost any other nerve will serve 

 as an afferent path. The gland may also, as we shall presently 

 explain, be called into activity by the cortex of the brain. 



It is certain that in the case of the submaxillary gland 

 secretion is not the direct result of increased blood-pressure. 

 It is not a case of filtration from the blood through certain 

 membranes and cells into the salivary duct. Atropin (bella- 



