TWENTY-SECOND ANNUAL MEETING. 



ON THE CLASSIFICATION OF THE SENSATIONS OF SMELL. 



(Critical.) 

 BY AV. S. FRANKLIN, STATE UNIVERSITY, LAWRENCE. 



The theory of the specific energy of the nerves is, that to each quality of sensa- 

 tion there are specific corresponding elements of the nervous system. The end 

 organs of these elements are so grouped and conditioned for each of the special 

 senses as to be exposed with advantage to a particular class of external stimuli. 

 However, any specific nerve group leads to the corresponding sensation when dis- 

 turbed by any physical means whatever. We think, then, of quality of sensation as 

 due to the particular nerve-cells that are excited, and not to the quality of the ex- 

 citement; indeed, all nervous activity seems to be alike in kind. 



Not only are the nerve elements of each of the five special senses specifically 

 distinct, but also some of the single senses comprehend a number of distinct groups 

 of specific nerve elements, each leading to a sensation more or less distinct. Thus 

 the sense of touch includes at least two separate senses, viz.: the sense of pressure 

 or of touch proper, and the sense of heat, each depending upon specific correspond- 

 ing nerve elements. There is also some reason for believing that the sensation of 

 cold corresponds to the excitement of a group of nerves distinct from those leading 

 to the sensation of heat. 



The sense of sight depends upon three specific groups of nerves. Their action, 

 however, is at variance with the above statement of the law of the specific energy 

 of the nerves, for a combined excitement of the three produces a single sensation 

 of color instead of three distinct, simultaneous, corresponding sensations; indeed, 

 that color sensations are triply manifold, is due to the fact that quality of color 

 depends upon the mixed excitement of these three specific groups. That this fact 

 does not weaken the theory of the specific energy of the nerves, is evident when we 

 consider that any sensation of particular significance tends to assuine a specific char- 

 acter as perceived by consciousness; indeed, any sensation, even if brought about by 

 the combined action of separate specific nerve elements, is perceived as a unit if it 

 has enjoyed a significance as a whole during our entire experience as a species, and 

 if there has been no occasion for the analysis of it by the higher centers (which in 

 fact may be impossible). This manner of attainment of a specific quality by a 

 sensation must depend upon the nervous organization in the higher centers, to- 

 gether with a specific cross-connection with the cells of the subordinate centers 

 upon which depend the more general qualities of the sensation in question. 



To whatever extent the theory of the specific energy of the nerves be true, it is 

 justifiable to assume that the quality of the sensations of smell depends upon the 

 action of specific nerves. The question remains whether the number and quality of 

 the sensations of smell depend upon the variable and mixed excitement of a few 

 specific nerve groups as in the case of color sensations, or whether there may be a 

 large number of specific nerve groups corresponding to as many characteristic odors, 

 and also whether the sensations of smell form a continuous manifoldness, and are 

 capable of systematic arrangement as are colors, or whether they are more or less 

 discrete and do not admit of such an arrangement. 



It seems that this question may be answered by considering the nature of the 

 external stimuli active in the sense of smell, as follows: 



Let us assume that the number and quality of smell sensations are dependent 

 upon the mixed action of but few specific groups, so that so far as the apparatus of 

 smell is concerned, it is possible for the sensations of smell to form a continuous 

 manifoldness of few dimensions; but the external stimuli of smell are discrete, and 



