140 PHYSIOLOGY CHAP. 



tendency develops to find pleasure in many other simple or 

 compound tastes, acid, bitter, or salt, so long as they are in weak 

 or moderately concentrated solutions. But the more or less 

 pleasant or unpleasant character of different flavours varies 

 according to the individual, and is in no necessary relation to the 

 nocuous or innocuous effects of the various foods. The proverb 

 that " what is good to eat can do no harm " only holds for those 

 food -stuffs that have already been physiologically selected. 



The affective tone concomitant with the taste sensations must 

 be carefully distinguished from those qualities of taste which we 

 perceive as a property of extraneous substances by which the 

 gustatory surface is specifically stimulated. 



In addition to the four primitive tastes we have been dis- 

 cussing sweet, bitter, acid, salt we commonly speak of a great 

 many other tastes by specific names, e.g. alkaline, metallic, astringent, 

 acrid, sharp, aromatic, alcoholic, fatty, slimy, dry, etc. Most of 

 these tastes, however, are found on physiological analysis to be 

 compound, i.e. they consist of several elementary constituents, in 

 which the sensations of taste are mingled with olfactory sensations, 

 and with the tactile, thermal, and pain sensations which are well 

 developed in the mucous membrane of the mouth. 



Chevreul (1824) first noticed the ease with which gustatory 

 sensations become associated with tactile and olfactory sensations, 

 owing to the great delicacy of tactile sensibility in the tongue 

 and the acute olfactory sensibility of the adjacent nasal mucous 

 membrane. Few substances are indifferent to the tactile and 

 thermal, sensory nerve-endings of the tongue, and so entirely 

 destitute of olfactory properties as to be unappreciable by smell. 



Physiological analysis enables us clearly to distinguish the 

 purely elementary qualities of taste in the innumerable gastro- 

 nomic flavours. 



It is easy to separate smell from taste ; if the nostrils are 

 closed, the aromatic, alcoholic, or nauseous flavours disappear. 

 The same occurs when olfactory sensibility is abolished by a 

 violent cold. In making a methodical experiment it is well to 

 blindfold the subject as well as to close his nose, to avoid visual 

 suggestion. It is then impossible by taste alone to distinguish the 

 aromas of different wines, of coffee, tea, chocolate, oil and butter, 

 various kinds of meat (Wing, Longet, Beclard), the alkaloids, such 

 as aconitine and nicotine (Richet and Gley), etc. But even after 

 absolute exclusion of smell the perception of the four tastes 

 known as primitive, i.e. sweet, bitter, acid, salt, remains un- 

 changed. 



The devices for separating thermal, tactile, and pain sensations 

 from those which are purely gustatory are more elaborate. To 

 exclude complication by thermal sensations, which introduce a 

 character of hot or cold, it suffices to warm the test solution to 



