If the body be very actively exercised, and a good deal of waste be effected by perspiration and exhalation from the lungs, the appetite becomes keener, and more urgent for immediate gratification; and if it is indulged, we eat with a relish unknown on other occasions, and afterwards experience a sensation of _bien-être_ or internal comfort pervading the frame, as if every individual part of the body were imbued with a feeling of contentment and satisfaction, the very opposite of the restless discomfort and depression which come upon us, and extend over the whole system, when appetite is disappointed. An amusing example of the principle here inculcated is to be found in the _Correspondance Inedite de Madame du Deffand_,[6] where she describes her friend Madame de Pequigni as an insatiable bustling little woman who consumes two hours every day in devouring her dinner, and “_eats like a wolf_.” But, then, remarks Madame du Deffand by way of explanation, “_Il est vrai qu’elle fait un exercice enragé_.” There is, in short, an obvious and active sympathy between the condition and bearing of the stomach and those of every part of the animal frame--in virtue of which, hunger is felt very keenly when the general system stands in urgent need of repair, and very moderately when no waste has been suffered. This principle is strikingly illustrated during recovery from a severe illness. “In convalescence from an acute disease,” as is well remarked by Brachet, “the stomach digests vigorously, and yet the individual is always hungry. This happens because all the wasted organs and tissues demand the means of repair, and demand them from the stomach, which has the charge of sending them; and, therefore, they keep up in it the continual sensation of want, which, however, is, in this case, only sympathetic of the state of the body.”[7] In alluding to this subject, Blaine observes, that “Hunger and thirst can only be satisfactorily explained by considering them as properties in the stomach by which it sympathizes with the wants of the constitution; and hence it is, that food taken in invigorates, even before it can be digested.”[8] Hence also the prostration of strength that is felt when the stomach has been for some time empty.