312 CONSTRICTOR AND DILATOR FIBRES. [Boon i. 



company with that nerve, and then ends partly on the tongue, 

 and partly in a small nerve which, leaving the lingual nerve before 

 reaching the tongue, runs along the duct of the sub-maxillary 

 gland, and is lost in the substance of the gland ; a small branch is 

 also given off to the sublingual gland. 



Now when the chorda tympani is simply divided no very 

 remarkable changes take place in the blood vessels of the gland, 

 v^but if the peripheral segment of the divided nerve, that still in 

 connection with the gland, be stimulated very marked results 

 follow. The small arteries of the gland become very much dilated 

 and the whole gland becomes flushed. (As we shall see later on 

 the gland at the same time secretes saliva copiously, but this does 

 not concern us just now.) Changes in the calibre of the blood 

 vessels are of course not so readily seen in a compact gland as in 

 a thin extended ear ; but if a fine tube be placed in one of the 

 small veins by which the blood returns from the gland, the effects 

 on the blood vessels of stimulating the chorda tympani become 

 very obvious. Before stimulation the blood trickles out in a thin 

 slow stream of a dark venous colour ; during stimulation the blood 

 rushes out in a rapid full stream, often with a distinct pulsation 

 and frequently of a colour which is still scarlet and arterial in spite 

 of the blood having traversed the capillaries of the gland ; the 

 blood rushes so rapidly through the widened blood vessels that it 

 has not time to undergo completely that change from arterial to 

 venous which normally occurs while the blood is traversing the 

 capillaries of the gland. This state of things may continue for 

 some time after the stimulation has ceased, but before long the flow 

 from the veins slackens, the issuing blood becomes darker and 

 venous, and eventually the circulation becomes normal. 



Obviously the chorda tympani contains fibres which we may 

 speak of as 'vaso-motor' since stimulation of them produces a 

 change in, brings about a movement in the blood vessels ; but 

 the change produced is of a character the very opposite to that 

 produced in the blood vessels of the ear by stimulation of the 

 cervical sympathetic. There stimulation of the nerve caused con- 

 traction of the muscular fibres, constriction of the small arteries ; 

 here stimulation of the nerve causes a widening of the arteries, 

 which widening is undoubtedly due to relaxation of the muscular 

 fibres. Hence we must distinguish between two kinds of vaso- 

 motor fibres, fibres the stimulation of which produces constriction, 

 vaso-constrictor fibres, and fibres the stimulation of which causes 

 the arteries to dilate, vaso-dilator fibres, the one kind being the 

 antagonist of the other. 



The reader can hardly fail to be struck with the analogy 

 between these two kinds of vaso-motor fibres on the one hand, and 

 the inhibitory and augmentor fibres of the heart on the other 

 hand. The augmentor cardiac fibres increase the rhythm and 

 the force of the heart beats ; the vaso-constrictor fibres increase 



