6 



Historical Introduction 



giving rise to this sensation. This sensation is rather the expression 

 of a general need created by the diminution of the total body fluid. 

 If one divides the oesophagus in the lower part of the neck in a 

 horse with bilateral parotid fistulae and then gives him water to 

 drink, with each swallow water is squirted out and is not absorbed 

 by the intestine. Under these circumstances the animal's thirst is 



Fig. 1.2. Claude Bernard in about i860. 

 (L'CEuvre de Claude Bernard, Bailliere, 1881.) 



not satisfied although the throat is kept moist and the animal con- 

 tinues to drink until exhausted . . . but if water is retained and 

 absorbed in the stomach and intestine, thirst is soon satisfied just 

 as it is by direct injection of water into the veins." 



Bernard investigated the nervous mechanisms of saliva secre- 

 tion, and showed that reflex secretion was produced by stimulation 

 of the central end of the lingual, facial and vagus nerves. He also 

 found that the secretion produced by application of sapid sub- 



