SECRETION OF SALIVA AND GASTRIC JUICE. 265 



bloodvessels only, and further that atropine, while it has no effect on the 

 latter, paralyzes* the former just as it paralyzes 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 substance of a muscular 

 fibre. Indeed, the two things, secreting activity and contracting activity, 

 are very parallel. 



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 BlattaJ, the evidence, as we have said, is as yet 

 not convincing. 



198. When the cervical sympathetic is stimulated, the vascular effects, 

 as we have already said ( 154), 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 veins. Sometimes, indeed, 

 the flow through the gland is almost arrested. The sympathetic, therefore, 

 acts as a vaso-constrictor nerve, and in this sense is antagonistic to the 

 chorda. 



As concerns the flow of saliva brought about by stimulation of the sym- 

 pathetic, in the case of the submaxillary gland of the dog the effects are 

 very peculiar. A slight flow results, and the saliva so secreted is remark- 

 ably viscid, of higher specific gravity, and richer in corpuscles and in the 

 above-mentioned amorphous lumps than is the chorda saliva. This action 

 of the sympathetic is little or not at all affected by atropine. 



In the submaxillary gland of the dog, then, the contrast between the 

 effects of chorda stimulation and those of sympathetic stimulation are very 

 marked ; the former gives rise to vascular dilatation with a copious flow of 

 fairly limpid saliva poor in solids, the latter to vascular constriction with a 

 scanty flow of viscid saliva richer in solids. And in other animals a simi- 

 lar contrast prevails, though with minor differences. Thus, in the rabbit 

 both chorda saliva and sympathetic saliva are limpid and free from mucus, 

 though the latter contains more proteids ; in the cat, chorda saliva is more 

 viscid than sympathetic saliva ; but in both these cases, as in the dog, stimu- 

 lation of the chorda causes a copious flow with dilated bloodvessels, and stimu- 

 lation of the sympathetic a scanty flow with vascular constriction. We shall 

 return again presently to these different actions of the two nerves; mean- 

 while we have seen enough of the history of the submaxillary gland to learn 

 that secretion in this instance is a reflex action, the efferent impulses of 

 which directly affect the secreting cells, and that the vascular phenomena 

 may assist, but are not the direct cause of the flow. 



199. We have dwelt long on this gland because it has been more 

 fruitfully studied than any other. But the nervous mechanisms of the other 

 salivary glands are in their main features similar. Thus the secretion of 

 the parotid gland, like that of the submaxillary, is governed by two sets of 

 fibres ; one of cerebro-spinal origin, running along the auriculo-temporal 

 branch of the fifth nerve, but originating possibly in the glosso-pharyngeal, 

 and the other of sympathetic origin coming from the cervical sympathetic. 

 Stimulation of the cerebro-spinal fibres produces a copious flow of limpid 

 saliva, free from mucus; stimulation of the cervical sympathetic gives rise 

 in the rabbit to a secretion also free from mucus, but rich in proteids and of 

 greater amylolytic power than the cerebro-spinal secretion ; in the dog little 

 or no secretion is produced, though, as we shall see later on, certain changes 



