20 R. C. GESTELAND AND OTHERS 



METHODS 



All of our experiments were done on the frog Rana pip lens. We used 

 either Ottoson's preparation (Ottoson, 1956) (a decorporate frog with 

 the olfactory mucosa exposed by removing the dorsal surface of the nasal 

 cavity), or a curarized frog with the same exposure. Responses of cells 

 appear to be the same with either preparation. However, the curarized 

 preparation with intact circulation is not as sensitive to overstimulation 

 and recovered from block caused by overstimulation more readily. 

 Furthermore, there is a curious transition in the responses of olfactory 

 receptors caused by the successive presentation of many odors. Most 

 of the cells lose their specificity and become responsive to all stimuH 

 or block and respond to none. This phenomenon does not occur as soon 

 when the animal has intact circulation. Some of the frogs had either 

 the first nerve or the ophthalmic branch of the fifth nerve, or both, sec- 

 tioned on one side. 



The animal was in a plastic box with a 1 cm x 2 cm hole for the electrodes 

 and the stimulator in the top directly over the exposed mucosa. The frog 

 was pinned to a cork block with a silver-silver chloride plate under his 

 head. Deodorized moist air flowed continuously through the chamber. 

 The box and cork were thoroughly washed and left exposed to laboratory 

 air between experiments and had no noticeable odor. 



The stimuli were small puff's of odorized air from 1 ml syringes, the 

 plungers of which were dipped in mineral oil or ethyl alcohol solutions of 

 reagent-grade (when available) organic chemicals. Odorized air blew 

 directly from the syringe onto the mucosa. There was no tubing as a 

 common path for the stimuli, as we found that it very rapidly adsorbed 

 odors and mixed them with successive ones. The odors of the stimulating 

 chemicals were easily recognizable, and no attempt was made to achieve 

 such purity that we could be sure that the odor was not due to impurities. 

 (We note the recent report that zone-refined skatole is odorless (Beynor 

 and Saunders, I960)). It is important to stress the significance of using 

 very low stimulus intensities. A puff" of 0.2 ml of odorized air lasting 1 sec 

 with the syringe tip 3 cm from the mucosa will typically evoke a larger 

 response from a unit that is sensitive to the particular odor. When 

 stimulus strengths are so large that two successive puffs cause a decrement 

 in the amplitude of the slow potential, the receptors will certainly be in 

 either a generally irritable or a blocked state, and no longer odor-selective. 



The EOG or Ottoson potential was monitored by a micropipette filled 

 with 3m KCl touching the surface of the mucosa, usually at the top of the 

 eminentia olfactoria. It indicates the arrival of the stimulus at the mucosa. 

 The maximum sensitivity of our recording system for the slow potentials 

 is approximately 0.2 mV for a noticeable deflection of the cathode-ray 

 tube beam. The negative-going Ottoson potential is preceded by a small 



