Absorption of Stimulus Energy 97 



effects of energy absorption. However, electrophysiological 

 studies with these preparations have only just started. 



Interesting work is now being done on the properties of 

 artificial membranes and the behavior of monomolecular films, 

 and it may very well be that this field of physical chemistry will 

 provide the questions — if not the answers — upon which to base 

 intelligent biophysical experimentation. For example, the mem- 

 brane alterations which account for an increased ionic conductance 

 are undoubtedly accompanied by shifts in molecular spacing, and 

 these may be diagnostically related to changes in intermolecular 

 bond strength (as measurable by alterations in tensile or compres- 

 sional strength of an axon), the ability of a membrane protein to 

 scatter light, or the absorption of incident light at a specific 

 wavelength. In view of the success which other physical tech- 

 niques, such as X-ray diffraction analysis, have brought to the 

 study of biological structure, these thoughts seem to be not unduly 

 optimistic. 



Summary 



We are only just beginning to inquire into the primary structural 

 changes which occur subsequent to the absorption of stimulus 

 energy at receptors. We may now state that the receptor mem- 

 brane appears to consist^fmultiple independent sites, all of which 

 contribute a small part to the overall electricaTTesponse effected 

 by the stimulus. However, we have very little idea of the mol- 

 ecular definition of the changes which result in the response. 

 Electrophysiological techniques will probably be i nsuffi cient for 

 the task of advancing this aspect of research on receptor mechan- 

 isms; and the advent of other physical approaches, having 

 considerably more resolution on the molecular scale of events, 

 seems inevitable. 



