Sensory Discrimination: The Chemical Sense 83 



to a chemical stimulus has a different conscious accom- 

 paniment from that of negative response to a mechanical 

 stimulus. The most natural interpretation of them all 

 on the psychic side is that of unpleasantness, increasing 

 in intensity as the reaction takes a more violent form.^ 

 The time occupied in reacting has, however, been made 

 a basis for differentiating the response to different chemi- 

 cals. It was found that if the worms were suspended 

 by threads, and their anterior ends dipped into solutions 

 of sodium, ammonium, lithium, and potassium chlorides, 

 the animals reacted to these substances with diminishing 

 promptness in the order just given. The differences in re- 

 action time were marked. Now all four of these substances 

 produce in man nearly the same taste quahty, salt, for 

 which the common constituent chlorine is therefore held 

 responsible. The sodium, hthium, ammonium, and po- 

 tassiimi ions have apparently but Uttle effect on the 

 human taste organs. Since the earthworm reacts with de- 

 cided time differences to the four, it may be that its taste 

 organs are specifically affected by each, and that different 

 taste qualities may be occasioned in its consciousness, sup- 

 posing it to be conscious (554). Kribs (410) has obtained 

 evidence of localized chemical sensibility in the annelid 

 .(Eolosoma; weak chemicals would produce a reaction 

 only if applied to the sensory hairs of the head end. Leeches 



^W. W. Norman argued that the squirming reactions of worms, and 

 the corresponding reactions of other animals to injurious stimulation, can- 

 not be taken as evidence of an accompaniment of disagreeable conscious- 

 ness, because of the fact that when the worm, for instance, is cut in two, 

 the squirming movements are confined to the posterior piece, while the head 

 end crawls away undisturbed. The head end, he urges, containing the 

 cerebral ganglia, ought to be the part capable of suffering, but it gives no 

 reaction (525). We cannot, however, conclude from the absence of a re- 

 action under abnormal conditions that when it occurs in the normal state 

 it has no conscious accompaniment. 



