1^8 'Journal of Comparative Neurology and Psychology. 



criminate between olfactory and gustatory sensations, but rather 

 elaborate physiological experimentation is necessary to enable us 

 to effect the analysis of these two sets of stimuli. Again, the 

 anatomical and physiological bases of several of the senses are 

 still very imperfectly known and in still other cases we are almost 

 wholly ignorant of the distinctive chemico-physical qualities of 

 the stimuli which call forth diverse sense modalities. The latter 

 point is notably true for the senses of smell and taste. The com- 

 mon statement that we smell substances only in the gaseous state 

 and taste liquids (solutions) is only approximately true, if at all, 

 in the mammals, and certainly cannot hold for the lowly aquatic 

 vertebrates where the differentiation of these two sense organs in 

 practically their definitive form first occurred. 



Attention has been drawn to the fact that, while tastes can be 

 classified under the four subjective quaUties, sweet, sour, bitter 

 and salty, the innumerable odors are apparently quite incapable 

 of any such classification. To this it may be added, on the one 

 hand, that Zwaardemaker claims to be able to classify the 

 known odors into some nine groups which he compares w^ith the 

 four classes of taste, and, on the other hand, that some recent 

 studies on the chemical physiology of taste^ go to show that it is 

 a reaction between the receiving organ and the ions of the sapid 

 substances and that the ions belonging to a given group, such 

 as those giving "salty" tastes, do not all produce the same 

 sensation quality. In other words, the four groups of taste 

 quahties, like the nine groups of smell qualities, are more or less 

 ill defined both from the standpoints of their psychological and 

 their physico-chemical criteria. It is to be expected that future 

 research will shed additional light on the physical and psycho- 

 logical criteria of smell and taste, but it will not eliminate their 

 strong similarity. 



These considerations suggest that smell and taste have origi- 

 nated phylogenetically from a common undifferentiated chemical 

 sense, a conclusion which is supported by the morphological rela- 

 tions of their cerebral centers. The details of this anatomical 

 evidence are far too complex to be summarized here and the reader 



1 L. Kahlenberg: The action of solutions on the sense of taste. Bui. Univ. Wisconsin, Science 

 iSer;ej, vol. 2, pp. 1-31. 1898. 



T. W. Richards: The relation of the taste of acids to their degree of dissociation. Am. Chemical 

 Journal. 1898. 



