NATURAL HISTORY. 89 



To erery shrub the warm effluvia cling, 

 Hang on the grass, im pregnant earth and skies, 

 With nostrils op ning wide, o er 1 .11 and dale, . 

 The vig rous hounds pursue.&quot; SOMERVILLE. 



example, -with musk, which is obtained from the musk-deer, a grain of which has 

 oeen kept freely exposed to the air of a room, whose doors and windows were kept 

 constantly open for a period of ten years, during which time the air, thus continually 

 changed, was completely impregnated with the odour of musk ; and yet, at the 

 end of that time, the particle was found to have not perceptibly diminished ir 

 weight. 



274. Why is a moist atmosphere the best for scent ? 

 Because moisture not only imbibes and holds the peculiar 



matters yielding the odour, but presents it to the nerves of smell, 

 which are spread out upon the internal chambers of the nose in 

 that state which is best adapted to impress the nerves. 



275. We know that just before rains set in, when the atmosphere is 

 humid, but not ivet, drains give forth unpleasant smells. Certain 

 bodies possess the property of exciting sensations of a peculiar nature, 

 which cannot be perceived by the organs of taste or touch, but seem to 

 depend upon the diffusion of the particles of the substances through 

 the surrounding air in a state of extreme minuteness. As the solubility 

 of a substance in liquid seems a necessary condition of its exciting the 

 sense of taste, so does its volatility or tendency to a vaporous state 

 appear requisite for its possession of odorous particles. 



276. Why is a wet day unfavourable for scent ? 



Because then the odorous effluvia becomes, as it were, &quot; drowned &quot; 

 by excess of moisture. It is absorbed and neutralised by water, 

 instead of being suspended in vapour. We know that persons having 

 colds, in which condition the mucous membranes of the nose are 

 in an extreme state of humidity, lose their power of smell. 



277. Why, when the ground is hard and the air dry, is there 

 little scent ? 



Because the vapour which serves as the rnenstrum of com 

 munication is absent, 



278. Wliy does scent sometimes lie breast high ? 



Because sometimes a stratum of humid air lies over the earth a 

 little above the surface. This arises from the difference between 

 the temperature of the earth and the air, and is frequently made 



