HUNGEK AND THERST. 21 



this somewhat probable, it is not apparent how it could be 

 demonstrated experimentally. It is undoubtedly the sympa- 

 thetic system of nerves which presides specially over nutri- 

 tion; and hunger, which depends upon deficiency of nutrition, 

 is certainly not conveyed to the brain by any of the cerebro- 

 spinal nerves. 



Thirst is the special sensation which induces the ingestion 

 of water. In its moderate development, this is usually an 

 indefinite feeling, accompanied with more or less sense of 

 dryness and heat of the throat and fauces, and sometimes, 

 after the ingestion of a quantity of very dry food, by a pecu- 

 liar sensation referred to the stomach. There is nothing 

 agreeable connected with the sensation of thirst under any 

 circumstances ; but when it has become intense, the imme- 

 diate satisfaction which follows the ingestion of a liquid, 

 particularly water, is very great. Thirst is very much under 

 the influence of habit, some persons only experiencing a de- 

 sire to take liquids two or three times daily, while others do so 

 much more frequently. The sensation is also sensibly influenced 

 by the condition of the atmosphere, as regards moisture, by 

 exercise, and other circumstances which influence the dis- 

 charge of water from the body, particularly by the skin. A 

 copious loss of blood is always followed by great thirst. This 

 we have frequently noticed in the inferior animals. After 

 an operation involving hemorrhage, they nearly always drink 

 with avidity as soon as released. In diseases which are 

 characterized by increased discharge of liquids, thirst is gen- 

 erally excessive. 



The demand on the part of the system for water is much 

 more imperative than for solids ; in this respect being only 

 second to the demand for oxygen. Animals will live much 

 longer deprived of solid food, but allowed to drink freely, 

 than if deprived of both food and drink. 1 A man, supplied 



1 It is a well-known fact that in inanition, the ingestion of water prolongs life, 

 in man and in the mammalia ; but the observations of Chossat have shown that 



