iv THE SENSE OF SMELL 189 



sensation of a mixed odour readily breaks up into its components, 

 and the phenomenon of conflict sets in; but theoretically it is 

 important that a sensation of new <[ii;ility ran, even temporarily, 

 be produced on mingling different and very dissimilar olfactory 

 stimuli. According to Nagel, this phenomenon presents a certain 

 analogy to what is observed for colours. 



IX. As regards the physiological value of olfactory sensations, 

 it should be noted that they not in frequently excite retlex acts, in 

 the motor system and in that of the glands, which may be 

 useful alike to the individual and to the species. 



\Ve have elsewhere seen that Pawlow noted a profuse salivary 

 and gastric secretion in the dog when the animal had merely 

 .sniffed at its food. We also pointed out the special importance to 

 the coming together and pairing of the sexes in many mammals 

 of the venereal odours that emanate from the mucous glands of the 

 sex -organs. Olfactory excitations undoubtedly play no incon- 

 siderable part in the sexual life of man. 



The repugnant smells that emanate from putrefying food- 

 stuffs, from excreta, and from certain poisonous substances induce 

 instinctive acts directed to the rejection of these substances for 

 food, or to removing or concealing them. At the same time it 

 must be noted that not all foul smells come from noxious matters, 

 nor do all noxious matters give off bad smells. 



There are close relations between the olfactory sensations and 

 the sphere of emotion. All odours that reflexly excite the 

 activities of vegetative and reproductive life constantly produce 

 a feeling of pleasure. But numbers of other olfactory sensations 

 are associated with a feeling of pleasure or distaste, without 

 connoting any physiological value or significance. These have 

 none the less a more or less definite psychical value. Smell is 

 perhaps more capable than any other modality of sensation of 

 profoundly altering that general affective state of the mind which 

 we call mood. Where there is a bad smell, one becomes impatient 

 and irritable ; in a pleasantly scented atmosphere the tone of the 

 mind alters, and we become cheerful or gay. 



Another characteristic of olfactory sensations is their capacity 

 of calling up by imagination the memory images of distant places, 

 objects or events with great clearness. Nagel notes that the 

 smell of tar calls up a seaport, the acrid smell of machine oil 

 revives the memory of a sea-voyage. 



In conclusion it is found that certain special olfactory 

 sensations sharpen the wits, and aid the processes of ideation and 

 judgment. The use and abuse of tobacco to which literary persons 

 are especially prone is partly justified by these psychically 

 stimulating effects. 



