26 R. C. GESTELAND AND OTHERS 



A few times, we have recorded from a metal microelectrode inserted in the 

 ophthalmic branch of the fifth nerve. Here also the spikes are of short 

 duration, and the units responded to the onset of heat with a decrease in 

 rate, and to turnoff of heat with an increase in rate compared with the 



Fig. 5. Resting discharge and responses to butyric acid and musk xylene. 



The large spikes have a short duration. The small spikes have the usual longer 



duration that is typical of olfactory receptors. Slow potentials are hardly visible 



because of low stimulus strength. Sweep lengths, 10 sec. 



resting rate. The units responded to touch with a rate increase. We did 

 not get responses to irritating chemicals but we have not tried often to 

 find such responses. Olfactory units recorded with the electrode as in the 

 usual preparation do not respond to small variations in temperature and 

 probably not to touch. 



The olfactory receptors are all odor-selective, that is, each one responds 

 to certain of the odors to which it is exposed and does not respond to 

 others. Most show a strong response to at least one of the twenty-five 

 odors that we have used and a weaker response to many more of them. 

 Figures 6-14 are examples of odor-specific responses of some of the cells 

 that we recorded. 



From these records and many more, we can suggest that there are some 

 patterns that are present in the responses of different cells, and we can 

 begin a list of the diff'erent groups of receptors. Our list is characterized 

 by extensive overlap, as if chemical names were not a good way to charac- 

 terize these types. However, odor properties do not seem to be any better. 

 One group responds vigorously to limonene, camphor, pinene, and some- 

 what less to carbon disulfide. A second responds to coumarin and musk. 

 Group three responds to butyric acid, valeric acid, mercaptoacetic acid, 



