200 ALBERT M. REESE 



tion still has a faintly sour taste to the human tongue in quantity, 

 but in the human eye produces no more sensation than cold 

 water. 



A .009375% solution produced in all animals a responses 

 though not a very decided one. Squirted upon the human 

 tongue this solution produces no sensation of acidity, though 

 in larger quantities a faintly sour taste may still be discerned. 



A .0046875 solution produced reactions in all animals, though 

 in most cases so slow that several pipettes full had to be squirted 

 upon the head before the animal withdrew. 



A .00234375% solution, containing about one part of the pure 

 acid to 42000 parts of distilled water, caused very slow responses, 

 and is probably about the limit of dilution that will cause response, 

 in these animals, though it is possible that under the proper con- 

 ditions they might be still more sensitive. It is only by alter- 

 nately drinking distilled water and the diluted acetic acid that a 

 sour taste can be discovered in such a great dilution. Without the 

 pure water for comparison the taste could not be detected, and 

 it would not be noticed even in this case unless it were being 

 tasted for. 



Experiment 8. As a chemical that would not naturally be 

 classed as sweet, sour, or bitter, but which produced a stinging 

 sensation, alcohol was used. 



10% ethyl alcohol, which produces a decided stinging sensa- 

 tion in the human mouth, caused a reaction with all the animals 

 tested (nine) both upon the head and upon the tail. The head 

 reactions were rather slow, and not as violent as might have 

 been expected, when the violence of the reactions to weak acids 

 and alkalies is remembered. The reactions from tail stimulation 

 were usually even slower, as would be expected, though they 

 were sometimes characterized by the biting motion mentioned 

 above. 



Only one of the nine animals reacted to 5% alcohol when the 

 tail was stimulated. Only one of the nine failed to react to that 

 grade of alcohol upon the head. Two of the latter reacted fairly 

 promptly, the rest very slowly, only after one or more entire 

 pipettes of alcohol had been squirted against the head. 



None of the animals reacted to 2,% alcohol when it was used 

 upon the tail, and only four of them reacted when the head was 



