156 PHYSIOLOGY CHAP. 



l>l;isni iii the cells of the taste -buds, or of the nerve-endings 

 distributed to them. To explain the fact that some papillae react 

 to a single taste, others to two, others to three, others again to all 

 the tastes, we must admit that the qualitative differentiation of 

 the gustatory sensibility of the epithelial cells or the nerve-endings 

 of the taste -buds is variously developed in different papillae. 

 The specifically dissimilar nature of the peripheral taste organs 

 also causes their dissimilar reaction to toxic substances. 



Oehrwall, on the strength of these results and of the fact 

 that the four primary tastes are discontinuous qualities which 

 cannot be arranged in series like musical tones of different pitch, 

 came to the conclusion that the four tastes cannot be considered 

 as different qualities of one sense, but are different modalities, i.e. 

 four distinct senses. In the same way the sensations of heat, 

 cold, and pressure, which were formerly considered to be different 

 qualities of one form of sensibility (the tactile sense), are now 

 recognised to lie different modalities of distinct senses. 



But the phenomena of contrast and compensation observed 

 between different gustatory sensations, as between different 

 colours, seem to contradict this theory of the plurality of gusta- 

 tory senses, since they show that the tastes are intimately 

 related to each other as different qualities of one modality of 

 sensation. 



Johannes Miiller noted that after masticating the root of the 

 aromatic calamus milk and coffee taste sour ; that sweet things 

 take away the flavour of wine, while cheese increases it. Oehrwall, 

 however, failed to confirm the first statement; generally speaking, 

 he found that bitter did not increase the sensibility to sweet. 

 On the other hand, he showed that sweet did not increase the 

 sensibility to acid, but considerably depressed it. 



The observation of Aducco and U. Mosso, that when a dilute 

 solution of sulphuric acid acts on the tongue for 5 to 10 minutes it 

 alters the organs of taste to such an extent that distilled water 

 is perceived as a very sweet fluid, is a more obvious contrast 

 phenomenon. If a dilute solution of quinine sulphate is applied 

 instead of distilled water, there is a sweet sensation at the tip of 

 the tongue, and the bitterness is only perceived at its base and 

 lateral edges. Solutions of formic, citric, and acetic acid do not 

 act like sulphuric acid ; hence the action of the latter is not 

 exclusively due to its acidity. 



Kiesow made a special study of contrast and showed that 

 after excitation of the tongue with weak solutions of hydrochloric 

 acid and salt distilled water is perceived as sweet. Laserstein 

 saw that after the action of a 1*5 per cent solution of soda 

 distilled water seems to be sweet. Nagel also found that on 

 washing out the mouth with a solution of potassium chloride 

 (which produces a faint taste of indefinite character) the gustatory 



