392 OP FOOD, AND THE DIGESTIVE PROCESS. 



When food is introduced into the stomach, the act of secretion is directly ex- 

 cited; the capillary vessels are gradually unloaded; and the immediate cause of 

 the impression on the nervous system is withdrawn. 1 By the conversion of the 

 alimentary matter into materials fit for the nutrition of the system, the remote 

 demand also is satisfied; and thus it is that the condition of the stomach, just 

 referred to, is permanently relieved by the ingestion of substances that can 

 serve as food. But if the ingested matter be not of a kind capable of solution 

 and assimilation, or the digestive apparatus cannot effect its preparation, the 

 feeling of hunger is only temporarily relieved, and soon returns in greater force 

 than before. The theory here given seems reconcilable with all that has been 

 said of the conditions of the sense of Hunger ; and particularly with what is 

 known of the effect produced upon it by nervous impressions, which have a pecu- 

 liar influence upon the capillary circulation. It also corresponds exactly with 

 what we know of the influence of the nervous system, and of mental impressions, 

 upon other secretions (CHAP. xiv. SECT. 6). 



414. The sense of Hunger, like other sensations, may not be taken cogni- 

 zance of by the Mind, if its attention be strongly directed towards other objects; 

 of this fact, almost every one engaged in active occupations, whether mental or 

 bodily, is occasionally conscious. The nocturnal student, who takes a light and 

 early evening meal, and, after devoting himself to his pursuits for several hours 

 uninterruptedly, retires to rest with a wearied head and an empty stomach, but 

 without the least sensation of hunger, is frequently prevented from sleeping by 

 an indescribable feeling of restlessness and deficiency, and the introduction of 

 a small quantity of food into the stomach will almost instantaneously allay this, 

 and procure comfortable rest. Many persons, again, who desire to take active 

 exercise before breakfast, are prevented from doing so by the lassitude and even 

 faintness which it induces, the bodily exercise increasing the demand for food, 

 whilst it draws off the attention from the sensation of hunger. 2 



415. The conditions of the sense of Thirst appear to be very analogous to 



the sense of Satiety is more dependent upon the continuity of these nerves than that of 

 Hunger ; for animals on whom the section of the Pneumogastric has been performed, do 

 not seem to know when they have had enough, but continue to gorge themselves with food 

 long after the stomach has been adequately filled. 



1 These views are confirmed by the observations of M. Bernard on the condition of the 

 gastric follicles during the intervals of their functional activity. He states that when the 

 stomach is empty, the follicles are lined by cylindrical epithelium of the same kind as that 

 which covers the general surface of the gastric mucous membrane ; and this even blocks up 

 their orifices, so that during fasting these appear as minute slightly prominent papillae. 

 The gastric fluid is contained in newly-formed cells which are rapidly generated and thrown 

 off, when the secreting process is called into renewed activity. ("Gaz. Med.," Mars, 1844.) 



2 The Author may be excused from mentioning the following circumstance, which some 

 years ago occurred to himself, and which seems to him a good illustration of the principle 

 that the sense of hunger originates in the condition of the general system, and that its 

 manifestation through a peculiar action in the stomach, is to be regarded as a secondary 

 phenomenon adapted, under ordinary circumstances, to arouse the mind to the actions 

 necessary for the supply of the physical wants but capable of being overlooked, if the 

 attention of the mind be otherwise directed. He was walking alone through a beautiful 

 country, and with much to occupy his mind ; and, having expected to meet with some 

 opportunity of obtaining refreshment on his road, he had taken no food since his breakfast. 

 This expectation, however, was not fulfilled ; but, as he felt no hunger, he thought little 

 of the disappointment. It was evening before he approached the place of his destination, 

 after having walked about twenty miles, resting frequently by the way ; and he then began 

 to feel a peculiar lassitude, different from ordinary fatigue, which rapidly increased, so that 

 during the last mile he could scarcely support himself. The "stimulus of necessity," 

 however, kept him up ; but on arriving at his temporary home, he immediately fainted. 

 It is obvious that, in this case, the occupation of the mind on the objects around, and on 

 its own thoughts, had prevented the usual warning of hunger from being perceived ; and 

 the effect which succeeded was exactly what was to be anticipated, from the exhaustion of 

 the supply of food occasioned by the active and prolonged exertion. 



