VARIETIES OF THE SENSES. 345 



appears to require the concurrence of a catalytic act of chemical com- 

 bination, between oxygen, or some other agent, and the odorous mat- 

 ter, at the surface of the olfactory membrane, to which, as we shall 

 hereafter describe, certain pointed appendages of the olfactory nerves 

 actually reach. Lastly in the third group are contained the thermic 

 and the photic senses, which convey to us the effects of those further 

 kinds of nndulatory movements, occurring between the molecules and 

 supposed intermolecular ether, or in the intermolecular ether itself 

 (or in the centres and periphery of those spheres of force, of which 

 matter, by some, is supposed to consist), upon which the phenomena 

 of heat and light are believed to depend, movements and phenomena 

 so far related, that, though heat may be manifested to us without light, 

 and light without heat, yet heat of a certain intensity is always accom- 

 panied by luminosity. These two senses we might group together as 

 the etheric senses. So regarded, the six senses may be thus arranged : 



Molar or Dynamical senses, . . 

 Molecular or Chemical senses, . . 

 Intermolecular or Etheric senses, . 



By means of these senses, all our knowledge of the matter and 

 energy of external nature is obtained, and all our psychical faculties 

 are called into action. In the absence of the most important senses, 

 indeed, man sinks intellectually below many animals. These six senses 

 necessarily correspond with those properties and actions, physical, 

 chemical, and material, of the world around us, which are cognizable 

 by us, and the effects of which, communicated to special recipient sur- 

 faces, must produce, through special mediating and translating appa- 

 ratus, corresponding changes in the nervous substance. It is now 

 generally believed that all the energic phenomena or manifestations 

 of force in nature, are correlated, or, as it were, capable of transform- 

 ation into each other: mechanical motion producing heat; heat, chem- 

 ical action ; both, in their turn, light, and so on ; so tha,t, according 

 to this view, the photic, thermic, chemical, and mechanical stimuli in 

 nature, are all correlated. In the same way, is it not probable that, 

 to receive, react against, and feel these various forms of correlated 

 stimuli, there may exist in the nervous system but one common func- 

 tional excitability, or one common and essential nervous energy, to 

 be excited by these stimuli; and if all active physical effects are to be 

 traced to different modes of motion, in the molecules or intermolecular 

 ether, in external, dead, non-nervous matter, may not all nervous 

 action, concerned in sensation, likewise depend upon different molecu- 

 lar and intermolecular modes of reaction, in internal, living, nervous 

 matter? 



On this, or some similar view, of a harmony between the physical 

 phenomena of external nature and the nervous reactions excited within 

 the sensorium, can we alone believe in, or explain the possibility of 

 our attaining accuracy and fixedness of knowledge concerning external 



