2 THE PHYSIOLOGY OF INSECT SENSES 



Pertinent details of an animal's environment are detected first 

 by utilizing the energy of particles to perform work in the biological 

 system. Thus, light is detected by virtue of an absorber which trans- 

 forms the energy of photons of certain specific energy. There is no 

 absorber to transform the energy of photons which, for example, 

 make up X-rays and gamma-rays. Heat is detected by absorbing the 

 energy of photons of a different energy level. Electricity is detected by 

 utiUzing the energy of electrons. Tastes and smells are detected by 

 utilizing the potential energy existing in the mutual attraction and 

 repulsion of the particles making up atoms. Sound is detected by 

 using the energy of moving particles of molecular size. 



A sense organ is a part of an organism specialized to receive a small 

 amount of energy from certain of the sources mentioned above and to 

 utiUze it to set off a train of events culminating in a nerve impulse. 

 Many cells and parts of cells do work with energy derived from the 

 sources mentioned. Many cells use the potential energy in carbo- 

 hydrates to do work, yet they are not sense organs. Certain of the cells 

 of green plants absorb photons of certain energies and perform work 

 much as the pigment rhodopsin of the eye absorbs protons and does 

 work. A sense cell differs from these in at least three major respects : 

 first, the work which is done by the sense cell is done at the expense of 

 its own potential energy, the energy of the environment is merely a 

 trigger; second, all sense organs, as far as we know, transform their 

 potential energy into electrical energy; third, they transmit this 

 electrical energy to another cell. And this energy, in turn, is transmitted 

 by an element which by itself could not have detected the original 

 environmental energy. 



A sense organ implies another element that will receive the change. 

 In this sense our attitude towards sense organs is teleological, but 

 there seems to be no escape from this attitude. As Granit (1955) has 

 concluded: Tor many purposes, e.g. physiochemical studies of 

 primary events, we can neglect the teleological aspects of the sensory 

 message and the general problem of central decoding of the code of 

 spikes, but I want to emphasize that research into special senses 

 differs from many other recognized branches of physiology in pre- 

 supposing and accepting the fact that understanding of biological 

 purpose is part of its aim, be it movement or perception. To close 

 one's eyes to this aspect of sensory physiology is to neglect the 

 biological, psychological, and philosophical implications of a branch 

 of natural science which actually is capable of giving some meaning 

 to "meaning' 



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