THE FUNDAMENTAL SUBSTRATES OF TASTE 129 



45 and 20 times the normal respectively. The effect on the sweet and sour 

 substrates was much less pronounced, it must however be pointed out 

 that 1 min after Eucupin no tartaric acid threshold could be obtained. 

 Nevertheless, there are anaesthetics which markedly influence the sensitivity 

 of all substrates. There are also some anaesthetics which exert a very strong 

 influence on the bitter substrate, while the other three substrates are rela- 

 tively much less influenced. The decisive factor here seems to be the sub- 

 stance itself, not its concentration. Indicating this is Acoin, which has as 

 much effect on the bitter substrate in a 0.03 m solution as 0.3 M Pantocain, 

 while the effect on the salty substrate is much higher with the latter than the 

 former. 



(b) Some experiments have shown that the length of time during which 

 the brushing-on of the anaesthetic is performed has a profound influence 

 on the effect. The longer the tongue is exposed to the anaesthetic, the 

 stronger is the effect. There is, of course, a limit to this, as an equilibrium 

 between supply of anaesthetic by brushing-on and removal through the 

 blood vessels is reached. 



(c) Immediately after the application of anaesthetic to the gustatory 

 field, the threshold increases and soon reaches a high level. The decrease 

 of sensitivity thus comes very fast, obviously in connection with a fast 

 entry through the epithelium of the tongue. Then not only the gustatory 

 but also the pressure receptors are affected. The effect on them however is 

 transient only. The original increased threshold decreases rapidly for 

 5 min and then decreases gradually until the original threshold to the test 

 substances is reached 15 to 80 min later. Of course there are differences 

 in this time course, depending mostly on the substrate but also on the 

 individual and the anaesthetic. Some features of this time course are 

 constant : at first a fast rise, then a fairly fast fall from the first to the fifth 

 minute, and at last a very gradual recovery. 



During the investigation it was found, as expected, that there are dif- 

 ferences between individuals, which are expressed quantitatively rather than 

 qualitatively. Thus the above presented sequence of susceptibility of the 

 four substrates varies. The susceptibility of the sweet substrate to 0.03 M 

 Pantocain was higher for taste subject 2 than for taste subject 1. The 

 threshold increase measured after 1 min was 30 in the first case, and 

 only 5 in the second. This individual difference in susceptibility is not 

 surprising, because in many investigations it has been proved that the 

 gustatory sense shows large individual differences. 



B. None of the chosen anaesthetics had a lingering effect, or a perma- 

 nently damaging one. Thus, basically it is a completely reversible effect. 

 A discussion is needed of the recovery time, however. The effect of a 

 variation in concentration is rather small. For example the recovery 

 time after 0.03 and 0.3 m Pantocain is 40 to 60 and 60 to 80 min respectively 



