342 JACQUES LE MAGNEN 



The basic experiment is the following. Twenty rats, living in individual 

 cages, receive daily two meals each lasting one hour, in which a constant 

 alimentary mixture is offered. This alimentary synthetic mixture is offered 

 in 2 forms, given alternatively in successive meals : the form A, consisting 

 of the diet flavoured by addition of a trace of an odorant, citral ; and the 

 form B, the same mixture flavoured by another odorant, eucalyptol. In a 

 group of 10 rats free intake of the form A is immediately followed by a 

 subcutaneous injection of a solution of glucose in an amount equivalent 

 to 25 per cent of the caloric intake in the preceding meal. In the same 

 animals, free intake of the other form of the food, flavoured with eucalyptol, 

 is associated with a postprandial administration of subcutaneous sahne. 

 In the other group of 10 rats intake of the form A (citral) is followed by 

 the administration of saline, and that of the form B (eucalyptol) is followed 

 by the subcutaneous injection of the glucose solution. After 21 days of 

 this treatment it was found that in a choice between the two forms the rat 

 exhibits a differential appetite. At that time the addition of citral to the 

 food for the animals of the first group, and of eucalyptol in the second 

 group, in a choice as well as in individually presented meals, reduced the 

 intake of the meal by 25 to 30 per cent. Thus at this time, differentiation 

 of the two flavours is the only basis for the specific appetite induced in a 

 quantitative manner by the conditioning postingestive action of glucose 

 during the preceding period. 



It is highly probable that physiologically also it is on the basis of the 

 natural flavours of foodstuffs and by accurate olfactory discrimination of 

 these flavours, that the animal learns its specific appetite, the refusal of non- 

 alimentary or toxic materials, and the acceptance of different foods in 

 accordance with their caloric and specific properties and in accordance 

 with metabolic needs. Concerning the role of offactory cues, another series 

 of experiments has shown the particular and privileged role played by 

 olfactory discrimination in this alimentary learning. The general procedure 

 in this series is the same as described above, except that the postin- 

 gestive conditioning factor is not glucose, but the addition to the mixture 

 of a small dose of D-amphetamine. This constant factor is in action in 

 5 groups of 20 rats each. In the first, an olfactory differentiation is estab- 

 lished between two forms of the mixture as before — the one associated 

 with the presence of amphetamine, the other not. In the second group a 

 differentiation of texture is offered to the rat by a difference in the granu- 

 losity of the sugar contained in the mixture. In the third group a difference 

 of luminosity (black-white) between the two forms is brought about by 

 addition to one of them of a black colorant. In the fourth group constant 

 position in the cage affords a possibility of discrimination of the two forms 

 by many complex spatial cues. The fifth group is a control in which no 

 sources of discrimination between the two forms are made available. Here 



