OLFACTORY IDENTIFICATION OF CHEMICAL UNITS 341 



This same hypothesis and somewhat arbitrary examples might be used to 

 explain all the above described phenomena of behavioural discrimination 

 of chemical units or mixtures, and also many data about masking, and 

 compensatory and reciprocal interactions of odours in mixtures. This 

 explicative value justifies such a hypothesis. It may also be regarded as an 

 indirect demonstration of the fecundity of Adrian's idea of a spatial- 

 temporal pattern of impulses as a productivity basis for discrimination of 

 odours. It may also serve as a reminder and as an illustration that the 

 correlation of peripheral patterns of discharge with behavioural discri- 

 minatory performance in olfaction, as in taste, is somewhat hopeless ; and 

 that therefor it may not be the proper basis for describing the discriminative 

 process at this level so as to account for behavioural data. The study of 

 more complex cortical and subcortical mechanisms which integrate and 

 regulate the peripheral messages might one day make possible this correla- 

 tion with behavioural data. 



We are shortly coming to the role of olfactory chemical analysis in dif- 

 ferent patterns of behaviour of animals. The intervention of olfactory 

 stimuli in behaviour, in preference to or in association with other sensory 

 modahties (especially vision), corresponds to and is always explained by 

 the ability to achieve by olfaction a biochemical analysis of the environ- 

 ment, a specific identification of a given molecule or of a given mixture of 

 molecules. The sources of stimuH for animals are as follows : their res- 

 piratory medium, their food, their sexual partners, their associates and 

 foes — that is to say the more fundamental elements concerned in their 

 individual survival and the survival of the species. 



In alimentary, sexual, social, warning and other behaviour where olfac- 

 tory cues are concerned, the identification of specific chemical materials is 

 always the basis for elementary reactions of attraction or repulsion, or for 

 more elaborate behaviour. The identification of the odour of its asso- 

 ciates in Phloxinus Levis (Goz, 1941), of the odour of its own young by the 

 mother in the rat (Beach, 1956) ; the discrimination in many species of 

 sexual odours (as I have shown in the rat : Le Magnen, 1952), the specific 

 warning effect of L-serine on the salmon (Brett and co-workers, 1952-54) : 

 all these are examples of the way in which olfactory stimuli and their 

 accurate identification are used by animals in determining behaviour. The 

 familiar behaviour of the dog able to follow an individual trail consisting 

 of infinitesimal traces of specific bodily odours absorbed on the soil, is the 

 simplest and best example of performances in which the olfactory molecular 

 analyser alone is concerned. 



In the field of my own work on regulation of food intake in the white 

 rat, I believe I have shown an example of the role of discrimination of 

 olfactory stimuli in the learning and manifestation by animals of specific 

 appetite in accordance with their metabolic needs. 



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