464 Comparative Animal Physiology 



sucrose, oxalic acid, and quinine hydrochloride. Many complex tastes can 

 be duplicated in this way, and some investigators claim to be able to dupH- 

 cate all tastes by such mixtures. In experiments of this type the influence 

 of other factors, especially of odors, must be carefully controlled. It can 

 readily be demonstrated that if the nose is held closed boiled turnips, apples, 

 and onions have almost the same taste, ham tastes Hke lamb, port wine like 

 sugar, and claret wine like weak vinegar. 



So far there is no record of a person being completely deficient in any 

 one of the four tastes, i.e., there are no known cases of partial "taste bhnd- 

 ness," although complete loss of taste may follow damage to the nervous 

 system. However, some persons are unable to taste certain bitter substances 

 to which others are quite sensitive. Snyder^*^ found that 68.5 per cent of 

 individuals tested could taste p-ethoxyphenyl thiourea, p-HOC6H4NH.CS.- 

 NH2, but that 31.5 per cent could not taste the substance. AbiHty to taste the 

 material is inherited as a non-sex-linked character. Comparable differences in 

 individual tasting ability are known for other materials.^*'' •^'* 



(a) 



AJ^J^U^^^^^yL 



l^) 



Fig. 151. Action potentials recorded from a single fiber ot the lingualis nerve of the 

 frog in response to stimulating the appropriate area of the tongue with 2 per cent (a) and 

 4 per cent (b) NaCl solution. Time is marked in 1/5 sec. From Pumphrey."^^" 



Many insects respond positively to sugars and it has been demonstrated, 

 using conditioning techniques, that Dytisciis trained to respond positively to 

 sucrose will respond in similar fashion to glucose and 20 other sugars or sugar 

 derivatives.'' Von Frisch-^-' found that all the sugars which are acceptable to 

 the bee have an additive stimulating effect. There seems to be little doubt that 

 the substances which taste sweet to man also give rise to a distinct sensation 

 in insects. 



The situation concerning the other taste modalities in the insects is not 

 at all clear. Dytisciis marginalis, Hydrous piceus, and related species learned 

 readily to distinguish between pairs of substances chosen from sucrose, NaCl, 

 HCl, acetic acid, and quinine, and could be trained to accept quinine 

 and avoid NaCl.'*- ^'^- •'"'" It was concluded that taste substances could 

 be classified into the same four groups for these beetles as for man. In bees 

 the stimulating effect is additive between NaCl and LiBr, NH4Br and HCl, 

 but not between quinine and acid. However, acids increased the repellency 

 of bitter substances such as aloin, arbutin, colocynthin, and salicin. It may 

 be said that for bees the taste substances fall into the four groups, but 



