ON THE OLFACTORY SENSE OF BIRDS 



117 



to teach birds to answer to an olfactory stimulus. A comparison of our 

 results with those of Zahn shows that it is very easy to be deceived by the 

 extraordinary power of optical discrimination of the birds. Our results are 

 in accordance with the recent findings of most other authors. 



The different species which we have tested all have an olfactory epithe- 

 lium, which, at least in the pigeon, is not degenerate, as our own histological 

 investigation has shown. Thus, there remains the existence of an olfactory 

 organ without any demonstrable function. It was then thought that it 

 might prove a fruitful line of research to look for spontaneous olfactory 

 responses without any attempt at training. Because of the secondary 

 olfactory pathways to the diencephalon, such spontaneous responses 

 might be expected to involve vegetative functions. 



SPONTANEOUS OLFACTORY RESPIRATION REACTIONS 



IN GEESE 



The experimental animal used for further studies was the greylag goose 

 {Anser anser L.). Seed-eaters do not have much use for an olfactory sense 

 in their search for and choice of food. In contrast to this, geese mostly 

 live on green plants, the safe choice of which surely is facilitated by a good 

 sense of smell. Also the olfactory epithelium is well developed, and, be- 

 cause of the size of the animals, it has a large area, which is of some signi- 

 ficance for the sense of smell (Neuhaus, 1957). 



Fig. 6. Schematic picture of apparatus for measuring respiratory reactions 

 to olfactory stimuli. 



The vegetative reaction studied was respiration, which is easily in- 

 fluenced by all sorts of factors. 



After the animals had got used to the experimenter they were made 

 familiar with the apparatus, which permitted recording of the respiration 

 without disturbing the animals (Fig. 6). The animal was seated comfort- 

 ably in a roomy nest. With a belt behind the shoulder joint a flat thin- 



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