CHAPTEE IV 



THE SENSE OF SMELL 



CONTENTS. 1. Peripheral organs and nerves of smell. 2. External mechanism 

 of olfactory function. 3. Excitation of smell by odorous substances in the form 

 of gas or of aqueous solutions. Electrical excitation of smell. 4. Chemical and 

 physical properties of odorous substances. 5. Classification of odours. 6. De- 

 termination of olfactory acuity (olfactometry and odorimetry). 7. Specific energy 

 of the olfactory apparatus deduced from the phenomena of partial anosmia and 

 partial olfactory fatigue. 8. Corrections and compensations of odours. 9. Physio- 

 logical and psychical value of olfactory sensations. Bibliography. 



THE sense of smell is much less important to human life than 

 to that of animals in general. Smell is but little developed in 

 Man in comparison with many other animals, as appears both from 

 the anatomical development of the olfactory bulb and the area to 

 which the olfactory nerve is distributed, and from its functions. 

 The olfactory apparatus of Carnivora attains such proportions that 

 in man it is in comparison a mere rudimentary organ. The 

 animal mind is dominated by a wealth of olfactory images, incom- 

 parably richer and more varied than those which man is capable 

 of conceiving. It may further be assumed that the range of 

 smells differs greatly for different kinds of animals. Herbivora 

 distinguish useful from injurious plants by their smell ; carnivora 

 are very insensitive to the odours of plants and flowers, but nave 

 a most acute and delicate perception of animal exhalations, by 

 which they follow the scent. The dog recognises the smell of his 

 master, showing that different individuals exhale different odours. 

 Hagen pointed out that different human races give off different 

 smells. Generally speaking, it may be affirmed that the most 

 essential needs of animal life, the satisfaction of the alimentary 

 want and of the sex instinct, are intimately connected with the 

 sense of smell. 



Man has a narrower and less specialised range of olfactory 

 sensation, but this does not exclude the fact that his capacity for 

 smell, particularly for certain odours, may reach a surprising 

 degree of sensibility. The olfactory sense seems to be more highly 

 developed among savage races than in civilised man. Humboldt 



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