CHAP, i.] DIGESTION. 261 



the latter, paralyses the former just as it paralyses the inhibitory 

 fibres of the vagus. Hence when the chorda is stimulated, there 

 pass down the nerve, in addition to impulses affecting the blood- 

 supply, impulses affecting directly the protoplasm of the secreting 

 cells, and calling it into action, just as similar impulses call into 

 action the contractility of the protoplasm of a muscular fibre. 

 Indeed the two things, secreting activity and contracting activity, 

 are quite parallel. We know that when a muscle contracts, its 

 blood-vessels dilate ; and just as by atropin the secreting action of 

 the gland may be isolated from the vascular dilation, so by urari 

 muscular contraction may be removed, and leave dilation of the 

 blood-vessels as the only effect of stimulating the muscular nerve. 

 In both cases the greater flow of blood may be an adjuvant to, but 

 is not the exciting cause of, the activity of the protoplasm. 



Since the chorda acts thus directly on the secreting cells, we 

 should expect to find an anatomical connection between the cells 

 and the nerve ; and some authors have maintained that the nerve- 

 fibres may be traced into the cells. But, save perhaps in the case of 

 certain glands of invertebrates (so called salivary glands of Blatta), 

 the evidence is as yet not convincing. 



When the cervical sympathetic is stimulated, the vascular 

 effects are the exact contrary of those seen when the chorda 

 is stimulated. The small arteries are constricted, and a small 

 quantity of dark venous blood escapes by the vein. Sometimes, 

 indeed, the flow through the gland is almost arrested. The sym- 

 pathetic therefore acts as a constrictor nerve, and in this sense is 

 antagonistic to the chorda. We have already referred to the 

 probable existence of a local vaso-motor centre situated in the 

 gland itself, in which indeed there are found ganglionic cells in 

 abundance. The fact that section of the cervical sympathetic does 

 not cause complete dilation of the vessels of the gland the dilating 

 effects of stimulation of the chorda being fully evident after pre- 

 vious section of the sympathetic affords additional support to this 

 view. We may accordingly suppose that, while the chorda tympani 

 inhibits, the sympathetic exalts, the action of this local centre. 



As concerns the flow of saliva brought about by stimulation of 

 the sympathetic, in the case of the submaxillary gland of the dog 

 the effects are very peculiar. A slight increase of flow is seen, but 

 this soon passes off, and so much saliva as is secreted is remarkably 

 viscid, of higher specific gravity, and richer in corpuscles and proto- 

 plasmic lumps, and is said to be more active on starch than the 

 chorda saliva. This action of the sympathetic is said not to be 

 affected by atropin. 



In the submaxillary gland of the dog then the contrast between 

 the effects of chorda stimulation and those of sympathetic stimu- 

 lation are very marked : the former gives rise to vascular dilation 

 with a copious flow of limpid saliva, the latter to vascular 

 constriction with a scanty flow of viscid saliva. And in other 



