194 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS times weaker than the preceding one. Stimuli of intermediate strength were obtained by altering the gas flows in each channel by a factor of three. In this way stimuli having concentrations covering up to four decades in half decade steps were available. The actual concentrations of stimuli were, of course, measured by the vapour monitoring system and this was done just before an experiment with a frog. Arbitrary units were used since for the purpose of the present investigation this was all that was necessary. In the case of certain odorants the lowest concentration gave fid signals obscured by noise and several readings had to be averaged to arrive at an estimate. An anaesthetized frog was prepared and placed in a head holder. The applicator was positioned with its nozzle pointing into the opened nasal cavity and about 4 mm away from it. The recording electrode was lowered by means of a micromanipulator so that its tip just touched the surface of the mucus overlying the eminentia olfactoria. The recordings required for this investigation were of the peak EOG voltages which are in fact reached soon after the onset of stimuli (see Fig. 1). Stimuli could therefore be switched off as soon as this peak voltage had been reached and doing this helped to minimize fatigue effects especially for strong stimuli. Also to combat fatigue 2 or 3 min were allowed for re- covery between each stimulation with the higher concentrations. The stimuli were usually applied in both ascending and descending order of concentration so that two EOG readings were obtained at each concen- tration. The odorant chemicals for which EOG data are reported in this paper are: Amyl acetate, 1,8 Cineole, Linalol, and Butyl acetate. RESULTS The results are shown entirely in the form of graphs on which all the experimentally determined points are plotted. These graphs are shown in Figs. 9-13. The abscissae in every case are the logarithms (base 10) of the concen- trations in arbitrary units of the stimuli used. The EOG amplitudes in milli- volts are plotted as the corresponding ordinates in Figs 9(a), 10(a), II(a),

RESPONSE 'OF THE FROG OLFACTORY SYSTEM 195 (b) I I I 'l Figure 9. (a) EOG (mY) v. log conch. Amyl acetate. EOG max = 7.9 mV. (b) log EOG v. log conch. Amyl acetate.