OLFACTORY IDENTIFICATION OF CHEMICAL UNITS 

 AND MIXTURES AND ITS ROLE IN BEHAVIOUR 



Jacques Le Magnen 

 College de France, Paris 



Electrophysiological investigation of olfactory and gustatory afferent 

 fibres does not, in our present state of knowledge, allow us to analyse the 

 discriminatory process itself. It is only behavioural data which actually 

 reveal whether a particular animal confuses two sugars and distinguishes 

 them from an acid ; or whether it has or has not the capacity to discrimi- 

 nate two molecules by smell, that is to say by their differential effects on the 

 olfactory system. Thanks, however, to the work of Adrian, Pfaffman and 

 of the Swedish and other workers, modern electrophysiological evidence 

 has given us an idea of both the physicochemical and the intrinsic 

 nervous mechanisms which, at different levels, account for the phenomena 

 demonstrated by behavioural methods. 



In this report on a very wide field of research, I shall limit myself to some 

 considerations and hypotheses suggested by comparing electrophysiological 

 and behavioural data about olfactory discrimination. Afterwards I shall 

 briefly draw attention to the part played in animal behaviour by chemical 

 analysis of the external world, using as an illustration some of my own 

 recent work on learning by rats of specific differential appetites. 



The division into four gustatory qualities is not exclusively the result of 

 subjective analysis in humans. This analysis in the human subject, more- 

 over, is less subjective than it seems, since it provides evidence through 

 objective responses that, for instance, two sugars are confused and add 

 their quantitative effects, that two acids are also confused and also add 

 their effects, etc. 



In many animal species, from invertebrates to man, behavioural methods 

 have confirmed the same phenomena ; of discrimination or no discrimina- 

 tion, of additivity or no additivity: it can thus be found out that in 

 aminals, also, the discriminative capacity of the gustatory system is limited 

 to the separation of four groups of stimuli — four groups plus a single 

 stimulus consisting of pure water, as we know through the elegant work of 

 Zotterman and his colleagues. This functional characteristic of taste, 

 permitting a rough analysis of the chemical medium in terms of four bio- 

 chemical properties of these stimuli, is a fundamental one. It provides a 



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