34 R. C. GESTELAND AND OTHERS 



that whether a receptor responds or not depends on the relative occupa- 

 tion of the different sites, or on occupation of a minimum number of sites 

 of more than one type. Some sites could be inhibitory, but it is not neces- 

 sary to postulate this in order to have a useful code without great numbers 

 of different cell species. 



At present, the fourth receptor model seems the most compatible with 

 our data, but we are in no position to settle the question yet. 



SUMMARY 



1. A new recording technique that allows the action potentials of single 

 primary olfactory receptors in the frog to be recorded extracellularly has 

 been described. 



2. The general response patterns of the olfactory receptors have been 

 described and correlated with the observations on the slow potentials of 

 the mucosa. 



3. Some of the odor-specific properties of the receptors have been 

 described. 



4. Possible receptor mechanisms have been discussed in the light of the 

 new data on odor-specific responses. 



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Beidler, L. M. and Tucker, D. 1955. Response of nasal epithelium to odor stimulation, 

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Beynor, J. H. and Saunders, R. A. 1960. Purification of organic materials by zone refin- 

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Le Gros Clark, W. E. 1957. Inquiries into the anatomical basis of olfactory discrimina- 

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Gesteland, R. C. 1961. Action Potentials Recorded from Olfactory Receptor Neurons, 

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Gesteland, R. C, Howland, B., Lettvin, J. Y. and Pitts, W. H. 1959. Comments on 

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