628 DIGESTION.. 



describable feeling of general indisposition ; sometimes accompanied 

 with one of circumgyration, either in the head or epigastric region ; 

 trembling of the lower lip, and copious flow of saliva. Along with 

 these signs, there is manifest diminution of the powers of the vascular 

 and nervous systems ; hence the utility of nauseating remedies when 

 these systems are inordinately excited. The causes, which produce 

 nausea, show that it may be either an external or internal sensation. 

 Those, that occasion it directly or externally, are emetics; too great 

 distension of the stomach, or the presence of food that disagrees by its 

 quality ; morbid secretions ; reflux of bile from the duodenum, &c. All 

 these are so many immediate irritants, which develope the sensation, as 

 external sensations in general are developed. In other cases, the cause 

 acts at a distance. Between the stomach and various organs of the 

 body, such extensive sympathetic relations exist, that if one be long 

 and painfully affected, the stomach sooner or later sympathizes ; and 

 nausea, or vomiting, or both are induced. In many instances, indeed, 

 the cause is much more remote than this ; the sight of a disgusting 

 object, an offensive smell, or a nauseous taste, will as certainly produce 

 the sensation as any of the more direct agents. To this class of causes 

 belongs the nausea produced by riding in a carriage with the back to 

 the horses, by swinging, and particularly by sailing on the ocean. How 

 the motion, which obviously excites the nausea in these cases, acts, has 

 been the subject of many speculations, especially as regards sea-sickness. 

 Darwin 1 refers it to an association with some affection of the organs 

 of vision, which, in the first instance, produces vertigo ; and M. Bourru, 

 in his French translation of the work of Gilchrist, " On the utility of 

 sea voyages in the cure of different diseases," ascribes it to irritation 

 of the optic nerves, caused by the impossibility of fixing the eyes on 

 objects soon after embarking. The objections to these views are, that 

 it ought to be prevented by simply covering the eyes, and that the blind 

 ought to be exempt from it, which is not the case. Dr. Wollaston 2 at- 

 tempted to explain it, by some change in the distribution of the blood ; 

 the descending motion of the vessel causing an accumulation in the 

 brain, as it causes the mercury to rise in the tube of a barometer. But 

 the explanation is too physical. The mercury, in an unyielding tube, 

 is readily influenced by the motions of the vessel ; but the blood in the 

 living animal is circumstanced far otherwise. It is under the influence 

 of a vital force, which interferes greatly with the action of purely physi- 

 cal causes. Were it otherwise, we should be liable to alarming accidents, 

 whenever the body is exposed to the slightest concussion. 



The generality of pathologists consider, that the first effect is upon 

 the brain, the sensation being produced consecutively through the in- 

 fluence of that organ on the stomach; and it is difficult not to accord 

 with this view; whilst it must be admitted, that the precise mode, in 

 which it is effected, is beyond our cognizance as in the case, indeed, 

 of every other phenomenon of the nervous system. In nausea, pro- 

 duced by the sight of a disgusting object, we have this catenation of 

 actions somewhat more clearly evidenced. The impression is manifestly, 



1 Zoonomia, iv. 252, 3d edit., Lond., 1801. 2 Philos. Transact, for 1810. 



