142 SMELL, TASTE, ALLIED SENSES 



of any one of which in a given compound would give it 

 a bitter taste. In dyes color-radicals have long been 

 called chromophores ; by analogy radicals concerned with 

 taste have been designated saprophores. Among these 

 are hydroxyl and the amine group. The nitro group NO2 

 is often associated, especially in aromatic compounds, 

 with a bitter taste. When three NO2 groups are included 

 in a given compound, it always has a bitter taste; when 

 two are at hand, the taste is conamonly bitter but not 

 invariably so; when only one such group is present, the 

 taste is not bitter. Thus the number of NO2 groups ap- 

 pears to be significant in the production of a bitter taste. 



The bitter taste, then, is excited by several classes of 

 substances; by ions that, with the possible exception of 

 the anion of picric acid, are apparently always cations 

 Herlitzka (1908), magnesium, ammonium, and calcium; 

 and by organic substances, especially the alkaloids, which 

 may act either through their molecules or through certain 

 atomic groups, the so-called saprophores. 



7. The Sweet Taste. The sweet taste is excited by 

 the diatomic and polyatomic alcohols of the aliphatic 

 series, by the aldehydes and ketons derived from these 

 alcohols, and especially by the hexoses whose polymeriza- 

 tion products, the disaccharides and polysaccharides, are 

 in this respect particularly important. Besides these 

 carbohydrates other organic compounds, such as chloro- 

 form, dextro-asparagine, and saccharine, have sweet 

 tastes. Among inorganic substances neutral acetate of 

 lead, often called sugar of lead, and the salts of glucinum 

 are known to be sweet. Solutions of the alkalis, if they 

 are of appropriate dilution, are said likewise to excite 

 this taste. 



