66 DON TUCKER 



presentation of clean air from the olfactometer. It is not known whether 

 this represents chemical, thermal, mechanical or other types of stimulation 

 of trigeminal receptors. However, for obvious mechanical stimulation the 

 individual action potential spikes are of much greater amplitude. 



The threshold concentration of amyl acetate for the rabbit's trigeminal 

 response falls in the same range as for the tortoise, namely 10-i-Ho 10- ^-^ of 

 saturation at 20°C. We have not yet found another odorant with as large 

 a spread between the olfactory and trigeminal threshold concentrations. 

 In fact, the trigeminal response probably appears first for the smaller mem- 

 bers of the aliphatic alcohol series. Integrated trigeminal responses to 

 alcohols are shown in Fig. 20 for the relatively crude stimulation technique 

 of free respiration into the mouth of a 125 ml Erlenmeyer flask containing a 





OCTANOL HEPTANOL HEXANOL PENTANOL 



PROPANOL ETHANOL METHANOL 



Fig. 20. Integrated trigeminal responses to alcohols. Free respiration and with 

 odor flash held before rabbit's nose for 1 min. 



small quantity of liquid odorant. The animal's respiratory rhythm was 

 unusually depressed, which caused exaggeration of the characteristic build- 

 up of the trigeminal response. The trigeminal receptors do not appear to 

 be so exposed to the gaseous environment in the nasal cavity as do the 

 olfactory receptors. However, the trigeminal response can approach its 

 limiting value within two or three inspirations in a preparation respiring 

 briskly. But in such instances the response frequently wanes and waxes 

 repeatedly with continuous application of the stimulus. 



The peak in trigeminal response to hexyl alcohol seen in Fig. 20 is typical. 

 In hvelier preparations octyl alcohol usually causes a small response. By 



