238 APPLIED PHYSIOLOGY 



juice ' by introducing substances into the mouth before 

 the meal is given. 



In this connection it is of interest to ask, What is 

 appetite, and can the physiologist give any explanation 

 of it? The reply is that the nature of the state of 

 feeling we call ' appetite ' is still very obscure. One 

 thing is certain namely, that it is not the same as 

 hunger. Hunger is the cry of the tissues for food, or, as 

 it has been put, 'the expression of the caloric require- 

 ments of the tissues,' and may be experienced even when 

 the stomach is quite full, as happens, for example, in the 

 case of a patient who has a fistula high up in the 

 ^testine. 



Appetite, on the other hand, is apparently more 

 dependent on sensations derived from the stomach itself, 

 and may be quite absent in cases of gastric disorder, even 

 although the patient be in a state of hunger. It has 

 been suggested, as already pointed out, that the sensa- 

 tions from the stomach on which appetite depends are 

 of a subconscious nature, and that a depression of them 

 may give rise to abolition of appetite (anorexia), whilst 

 their exaltation may produce an excessive desire for food 

 (bulimia). 



How long the flow of 'appetite juice' lasts in normal 

 feeding it is impossible to say, but very soon the second 

 or chemical method of excitation comes into play. This 

 is brought about by the action of certain chemical con- 

 stituents of the food on the nerves of the stomach. Not 

 all nutritive substances are able to excite the gastric 

 nerves. The most powerful are the extractives of flesh, 

 dextrins, milk, and water. 



