NOTES 



A NOTE ON THE SUPPOSED OLFACTORY HUNTING- 

 RESPONSES OF THE DOG 



H. M. JOHNSON 



Nela Research Laboratory, National Lamp Works of General Electric Co., Nela 



Park, Cleveland Ohio. 



Our present inability to measure or control olfactory stimuli 

 may have some bearing on the fact that the dog's sense of smell 

 has been avoided by careful experimental investigators. A 

 number of problems in this field are highly interesting even though 

 they do not lend themselves to treatment by quantitative 

 methods. The supposed olfactory responses made by the dog 

 in hunting are especially puzzling. At present the only available 

 data are purely anecdotal, and these are meager, conflicting and 

 untrustworthy. 



Various assertions have been made as to the ability of the 

 trained hunting-dog to trail his quarry. The belief is wide- 

 spread that the bloodhound can follow a trail over 24 hours old 

 without back-tracking. Let us accept provisionally a seemingly 

 conservative statement; that a fox-hound can follow a three- 

 hour-old trail of a rabbit without back-tracking, and assume 

 that this is very near the limit of the dog's ability. A casual 

 examination suffices to show the difficulty of explaining the dog's 

 behavior. 



Many hunters have said in effect that the dog follows the 

 trail in the direction taken by the rabbit because the tracks made 

 recently excite more intense smell-processes than do the older 

 tracks. This explanation is not satisfactory. Suppose that in 

 each of a series of tracks, a, b, c, etc., a like quantity of the same 

 single sme 1-substance had been deposited by the rabbit; that 

 the tracks had been made one second apart, and that a was made 

 three hours ago. It is evident {changes of chemical composition 

 being excluded) that the smell-substance is greatest in quantity 

 when first deposited. It becomes dissipated in time so that in 

 this case there is barely enough left in the track a to affect the 

 dog. 



If the smell-substance is deposited in a gaseous state, its 



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