RESPONSES TO ODORANTS 61 



respond readily, but amyl acetate is an exception. Although the vomero- 

 nasal response to amyl acetate tends to be small, it appears shortly after the 

 olfactory response with increase of concentration. On the other hand, the 

 trigeminal response has a well-defined threshold lying between 10~^'^and 

 10"i-o of amyl acetate at saturation. This is one reason why amyl acetate 

 has proved so useful in our work, for nearly all the reflex effects under 

 anesthesia that we have seen appear to be stimulated by trigeminal activity. 

 In the discussion of Fig. 13, it was noted that for the receptors being 

 monitored, the olfactory accessibility was greater during the benzyl amine 

 run than during the amyl acetate run. The trigeminal response exhibited a 

 strong flow rate dependence as did the olfactory response, but the trige- 

 minal response appeared first either with increase in concentration of 

 benzyl amine or increase of nasal flow rate. We believe that the cause of 

 the change in olfactory accessibility was due to changes in the nose pro- 

 duced by reflexes in response to trigeminal receptor stimulation. A similar 

 change in olfactory accessibility was often seen for temperature in the 

 range of 10-15°C. 



An important mechanism for variation of olfactory accessibihty is surely 

 the changing of physical dimensions within the nasal cavities. Such a 

 change can be demonstrated by stimulating electrically the cervical sym- 

 pathetic nerve in a preparation with a window in the top of the nose. The 

 size of the aperture between the vestibular chamber and the olfactory 

 cavity proper is reduced markedly with activation of the sympathetic 

 effectors. The eff'ect on the olfactory response to an odorous stimulus of 

 constant parameters at the level of the naris is shown in Fig. 15. 



w*WS.*-N»A-.^-*- Wi W '^ "^^"^^ ^"^ *'*-' W^ V.K, ^ ^ 



Fig. 15. Reduction of phasic and tonic olfactory responses caused by electrical 

 stimulation (bars) of the cervical sympathetic nerve. Constant flow through the 

 nose at 1 msec and amyl acetate concentration in air held at 10"--^ of saturation. 



Amyl acetate concentration was varied up through 10~i'^ of saturation 

 for the records of the mucosal potential shown in Fig. 7. The electrode 

 invariably lost contact with the mucosa whenever 10^^-^ amyl acetate was 



