SMELL AND TASTE 367 



of musk is delivered to one side of the brain, the sensation of 

 bitter almonds to the other ; but when attention is directed to 

 these two sensations there is found a quality in the one which 

 is irreconcilable with the quality of the other. 



In certain persons and under certain pathological conditions, 

 sensitiveness to particular odours, or groups of odours, is 

 absent, while for the rest the sense is normal. Methylated 

 spirit, prussic acid and mignonette, constitute a group which 

 not infrequently drops out. Instances have also been reported 

 of persons unable to smell vanilla (to which some are hyper- 

 sensitive), and of others insensitive to violets, although 

 normally sensitive to the scents of other flowers. The notes 

 sounded in consciousness extend over a long gamut ; but there 

 are reasons for thinking that the number of keys on the clavier 

 which odoriferous substances strike is limited. Eleven is the 

 number provisionally adopted. The effect in consciousness 

 varies according as one key or another is struck, or several at 

 the same time with varying degrees of force. 



Many attempts have been made to associate the sensation- 

 qualities of the various odours with the chemical or physical 

 properties of their odorants, with but little success as yet. To 

 excite the sense of smell, a gas must be at least a little heavier 

 than air. No volatile body, it is stated, is so heavy as to be 

 odourless ; on the contrary, speaking generally, heavy molecules 

 are more stimulating than light. The quality of a smell-sensa- 

 tion would therefore appear to depend upon the period of vibra- 

 tion of the molecules of the substance which evokes it ; but, as 

 already stated, a consideration of the apparatus which responds 

 to stimulation by odoriferous particles does not help us to an 

 understanding of the way in which the particles act upon it. 



Taste is far more limited in its range of sensations than smell. 

 The back of the tongue is sensitive to bitters, the tip to sweets 

 and salts, the sides to acids. Mixtures of these qualities are 

 distinctly analysable by the sense of taste. Our sensations of 

 taste do not fuse. Slight differences in the way in which the 

 organs on the different parts of the tongue react to stimulation 

 enable us to recognize that a sapid substance is a mixture. 

 When, with a great flourish of trumpets, saccharin was intro- 

 duced as a safe sweetener for gouty people, an attempt was 

 made to provide them with saccharin-sweetened jam. The 



