HUNGER AND THIRST 141 



only two or three times daily, while others do so much more frequently. 

 The sensation is also sensibly influenced by the condition of the atmos- 

 phere as regards moisture, by exercise and by other conditions that 

 influence the discharge of water from the body, particularly by the skin. 

 A copious loss of blood is always followed by intense thirst ; and in 

 diseases characterized by increased discharge of liquids, thirst usually is 

 excessive. 



The demand on the part of the system for water is much more im- 

 perative than for solids ; and in this respect it is second only to the demand 

 for oxygen. Animals live much longer when deprived of solid food but 

 allowed to drink freely than if deprived of both food and drink. A man, 

 supplied with dry food but deprived of water, will not survive more 

 than a few days. Water is necessary to the processes of nutrition, and 

 acts, moreover, as a solvent in removing from the system the products 

 of katabolism. 



After deprivation of water for a considerable time, the intense thirst 

 becomes most distressing. The dryness and heat of the throat and 

 fauces are increased and accompanied with a sense of constriction. A 

 general febrile condition supervenes, the blood is diminished in quan- 

 tity and becomes thickened, the urine is scanty and scalding, and 

 there seems to be a condition of the principal viscera approaching 

 inflammation. Death takes place in a few days, usually preceded by 

 delirium. 



The sensation of thirst is instinctively referred to the mouth, throat 

 and fauces ; but it is not appeased necessarily by the passage of water 

 over these parts, and it may be effectually relieved by the introduction 

 of water into the system by other channels, as by injecting it into the 

 veins. Bernard has demonstrated, by the following experiment, that 

 water must be absorbed before the demands of the system can be satis- 

 fied : He made a section of the oesophagus in a horse, tied the lower 

 opening and allowed the animal to drink after he" had been deprived of 

 water for a number of hours. The animal drank an immense quantity, 

 but the water did not pass into the stomach and the thirst was not re- 

 lieved. He modified this experiment by causing dogs to drink, with a 

 fistulous opening into the stomach by which the water was immediately 

 discharged. They continued to drink without being satisfied, until the 

 fistula was closed and the water could be absorbed. In a case reported 

 by Gairdner (1820), in the human subject, all the liquids swallowed 

 passed out at a wound in the neck, by which the oesophagus had 

 been cut across. The thirst in this case was insatiable, although 

 buckets of water were taken in the day ; but on injecting water into 

 the stomach, the sensation was soon relieved. 



