RESPONSES TO ODORANTS 59 



More correctly, one should use double-subscript notation to identify both 

 the kinds of site and kinds of odorant. The numerical values found for the 

 constants in the equation are 



Ki = 17,800 reciprocal concentration units 

 and K2 — 274 reciprocal concentration units, 



where the unit of concentration is air saturated at 20 C with amyl acetate. 

 It would be valuable if a way could be found to determine the absolute 

 value of response in terms of nerve impulses per receptor and unit of time. 

 Dr. Shibuya's current work in our laboratory may point the way to this 

 goal. 



(c) Aqueous solutions of odorants. Systematic study showed that the 

 minimum requirements for a solution to approximate the normal mucous 

 environment of the receptors is osmotic pressure about equal to that of the 

 blood and the presence of calcium ions. The solution devised for Gopherus 

 contains 1.4 mM CaClg and 0.17 m NaCl or its osmotic equivalent of 

 sucrose. Freshly made solutions invariably contained contaminating 

 odorants. Slow percolation through activated cocoanut charcoal, pre- 

 viously equiUbrated with the solution, reduced odorous contamination to 

 tolerable levels. The subject of unwanted odors is highly practical and 

 has not received the attention due it, but the whole of this paper could 

 easily be devoted to the topic. 



Olfactory receptors were found to be insensitive to variation of ionic 

 strength, to variation of pH over several units and to variation of osmotic 

 pressure over a range of about zb 20-25 per cent. Increase of calcium ion 

 concentration to many times the 1.4 mM level had neghgible effect on the 

 background neural activity (contaminating odorants?), but with decrease 

 below that level the activity rose rapidly. Solution free of calcium ions 

 flowed continuously through the olfactory cavity initially causes intense 

 receptor activity and after a few minutes the receptors are killed. The 

 animal's freshly spilled blood is intensely stimulating to the olfactory 

 receptors, but no harm seems to be done. Bleeding occurs when the 

 opening to the olfactory cavity is made in the top of the nose (Fig. 1). 



Aqueous solutions were introduced through the cannula in the choana 

 and flowed out the window in the top of the nose. The naris was plugged 

 loosely with cotton. Cleaned solution medium was used to make up various 

 concentrations of odorants. Control apparatus was arranged to alternate 

 the flow between solutions with and without added odorant. The records 

 obtained in these experiments were remarkably similar to those taken with 

 the same odorants introduced in the gaseous phase. Vomeronasal and 

 olfactory responses recorded simultaneously are shown in Fig. 14. The 



