276 OF FOOD AND THE DIGESTIVE PROCESS. 



to replenish the system. The proper intimation is the pleasurable sen- 

 sation which is experienced, when the cravings of the appetite are first 

 allayed ; since, if the stomach be sufficiently distended with wholesome 

 food for this to be the case, it is next to certain that the digestion of 

 that food will supply what is required for the nutrition of the body. It 

 is only when the substance with which the stomach is distended, is not 

 of a digestible character, that the feelings excited by the state of that 

 organ are anything but a correct index of the wants of the system. 



487. The Par Vagum is evidently the nerve, which conveys to the 

 sensorium the impression of the state of the stomach, and which is 

 therefore the immediate excitor of the sensation of hunger, or of the 

 feeling of satiety. But it is evident from experiments upon animals, 

 that it is not the only source, through which they are incited to take 

 food, and are informed when they have ingested enough ; and it is 

 probable that the Sympathetic nerve is the channel, through which the 

 wants of the system are made known, and through which, in particular, 

 the feeling of general exhaustion is excited, that is experienced when 

 there has been an unusual waste, or when the proper supply has been 

 too long withheld. 



488. The conditions of the sense of Thirst are very analogous to 

 those of hunger ; that is, it indicates the deficiency of fluid in the body 

 at large ; but the immediate seat of the feeling is a part of the ali- 

 mentary canal, not the stomach, however, but the fauces. It is re- 

 lieved by the introduction of fluid into the circulating system, through 

 any channel ; whilst the mere contact of fluids with the surface to 

 which the sensation is referred, produces only a temporary effect, un- 

 less absorption take place. If liquids be introduced into the stomach 

 by an oesophagus-tube, they are just as effectual in allaying thirst, as 

 if they were swallowed in the ordinary manner ; and the same result 

 follows the injection of fluid into the veins (as was most remarkably 

 the case when this method of treatment was practised in the Asiatic 

 Cholera), or the absorption of fluid through the skin or the lower part 

 of the alimentary canal. 'The deficiency of fluid in the body may 

 arise, and Thirst may consequently be induced, either by an un- 

 usually small supply of fluid, or by excessive loss of the fluids of the 

 body, as by perspiration, diarrhoea, &c. But it may also be occasioned 

 by the impression made by particular kinds of food or drink upon the 

 alimentary canal ; thus salted or highly-spiced meat, fermented liquors 

 when too little diluted, and other similar irritating agents, excite thirst ; 

 the purpose of which sensation is evidently to cause the ingestion of 

 fluid, by which these substances may be diluted, and their irritating 

 action prevented. 



