204 THE SENSES OF ANIMALS 



be more appropriately likened to flower-buds than bulbs. 

 They consist of a cluster of cells, representing the petals, 

 surrounding the receptor cells the ends of which project as 

 fine threads, and might represent stamens and stigma. The 

 ends of the taste-nerves ramify round the bases of the receptor 

 cells, and convey signals towards the brain when the receptors 

 are changed chemically by the contact of tasteable substances 

 in solution. 



There are only four tastes to which our taste-bulbs respond 

 — sweet, sour, bitter and salt. Other animals may, of course, 

 taste a greater or lesser number of tastes but of that we know 

 nothing, although it is unlikely that the other mammals 

 differ from us, whatever may be the case with other verte- 

 brates, and still more with the invertebrates. Whenever we 

 enjoy a meal we realize, if we take the trouble to think about 

 it, that we are aware of much more than the four tastes, in 

 fact the enjoyment comes from all the delicious and varied 

 flavours rather than from the four basic tastes. The flavours, 

 however, are not tasted but smelt; they diffuse from the 

 mouth into the air at the back of the nose and act upon the 

 endings of the smell nerves there. If you have a really bad 

 cold, so that the smell receptors are completely blanketed, 

 the most fragrant cup of Brazilian coffee merely tastes bitter- 

 sweet if you take sugar, or just bitter if you don't. In similar 

 conditions it is said that you cannot distinguish between an 

 apple and an onion, apart from the sweet or sour of the apple. 

 There is, however, more to food than just taste and flavour; 

 its texture, which is perceived by the touch receptors that 

 are numerous in the tongue, is of almost equal importance 

 — was not H. G. Wells's Mr. Polly turned from suicide by 

 the mention of savoury fried bacon, all steaming hot and 

 crisp? It was the "crisp" that did it. 



Each taste-bulb generally responds only to one kind of 

 taste, and the bulbs are arranged on the tongue mainly in 

 groups of a kind — those for sweet are mostly at the tip, and 

 those for bitter mostly at the back. You can chew up a 

 quinine tablet with the front teeth, keeping the bits at the 

 front of the mouth with the tip of the tongue, without tasting 

 the intense bitterness. If you wash it down quickly with a 

 draught of water so that it rapidly swishes over the back of 



