HUNGER AND THIRST. 165 



It is evident, from the amount of matter that is daily discharged from 

 the body, that the process of disassimilation must be very active. Its constant 

 operation necessitates a constant appropriation of new matter by the parts, 

 in order that they may maintain their integrity of composition and be al- 

 ways ready to perform their offices in the economy. The blood contains 

 all the materials necessary for the regeneration of the organism. Its inor- 

 ganic constituents are found generally in the form in which they exist in 

 the substance of the tissues ; but the organic constituents of the parts are 

 formed in the substance of the tissues themselves, by a transformation of 

 matters furnished by the blood. The physiological wear of the organism is, 

 therefore, being constantly repaired by the blood ; but in order to keep the 

 great nutritive fluid from becoming impoverished, the matters which it is 

 constantly losing must be supplied from some source out of the body, and 

 this necessitates the ingestion of articles which are known as food. Food is 

 taken into the body in obedience to a want on the part of the system, which 

 is expressed by the sensation of hunger, when it relates to solid or semi-solid 

 matters, and of thirst, when it relates to water. 



HUNGER AND THIEST. 



The term hunger may be applied to all degrees of that peculiar want felt 

 by the system, which leads to the ingestion of nutritive substances. Its 

 first manifestations are, perhaps, best expressed by the term appetite ; a sen- 

 sation by no means disagreeable, and one which may be excited by the sight, 

 smell, or even the recollection of savory articles, at times when it does not 

 absolutely depend on a want in the system. In the ordinary and moderate 

 development of the appetite, it is impossible to say that the sensation is refer- 

 able to any distinct part or organ. It is influenced in some degree by habit ; 

 in many persons, the feeling being experienced at or near the hours when 'food 

 is ordinarily taken. If not soon gratified, the appetite is rapidly intensified 

 until it becomes actual hunger. Except when the quantity of food taken is 

 unnecessarily large, the appetite simply disappears on the introduction of 

 food into the stomach and gives place to the sense of satisfaction which 

 accompanies the undisturbed and normal action of the digestive organs ; or 

 in those who are in the habit of engaging in absorbing occupations at that 

 time, the only change experienced is the absence of desire for food. 



It has been observed that children and old persons do not endure depri- 

 vation of food so well as adults. This was noted in the case of the wreck 

 of the frigate Medusa. After the wreck, one hundred and fifty persons, of 

 all ages, were exposed on a raft for thirteen days, with hardly any food. Out 

 of this number only fifteen survived ; and the children, the young persons 

 and the aged, were the first to succumb. 



Important modifications in the appetite are due to temperature. In cold 

 climates and during the winter season in all climates, the desire for food is 

 notably increased, and the tastes are somewhat modified. Animal food, and 

 particularly fats, are more agreeable at that time, and the quantity of nutri- 

 ment which is demanded by the system is then considerably increased. In 



