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Preface 



In the past several years considerable progress has been made mThe-rfa*rT- 

 fication of the problems of neural activity and of a host of ancillary physical 

 and chemical events in living cells. Investigators in many fields from bi- 

 ology through chemistry, physics, mathematics, philosophy and psychology, 

 have contributed new observations and concepts. They have drawn upon one 

 another's knowledge and experience in attempts to refine existing experimental 

 techniques and arrive at more accurate estimates of the properties and inter- 

 relationships of particular structures, mechanisms and processes at levels from 

 the grossest complexity of the organism in toto to the most microscopic and 

 sub-microscopic complexities of molecular structure and orientation. 



Consequently, it was felt that there was need for some discussion of stimulus- 

 response problems not only insofar as existing data are concerned, but more 

 particularly in relation to whether or not present experimentation and concept 

 are leading to better understanding of the crucial problems underlying neuronal 

 behavior. 



The existence of certain transient phenomena in nerve cells forms the basis 

 for their physiology and confronts the investigator with certain sorts of prob- 

 lems which, although they are not unique to this field, are representative of the 

 difficulties involved in relating biological function to molecular interaction. The 

 reduction of experimental observations to a molecular level must involve, first 

 of all, a recognition that a rather small number of molecular units are involved 

 in the events leading to the initiation of excitation in an excitable system, and 

 that, therefore, the possibility exists that ordinary statistical considerations 

 may not apply. 



In seeking both the proper questions and answers, one is confronted at the 

 outset with the initial way station of reception — the input to the nervous sys- 

 tem. The major questions asked are how, in general, physical stimuli are trans- 

 duced into nervous excitation; and is the principle reaction chemical or physical? 

 In other words, how are stimuli transformed into meaningful, information- 

 carrying nervous messages? It should be pointed out that while there is no re- 

 quirement that transduction imply some analogy with mechano-electrical de- 

 vices, it is suggested that an important property which must be inherent in 

 a receptor is some means of converting the energy incident upon it into nervous 

 excitation. The second question, which appears to stress a somewhat unreal 

 dichotomy, is less clear in that a distinction between biophysical and biochem- 

 ical reactions is less and less obvious as the units under consideration approach 

 molecular dimensions. 



Impulses from the receptors are passed on to aggregates of neurons in the 

 central nervous system. At this level one would like to know if any progress has 



