THE SPECIAL SENSES 283 



fluids, or with solids in solution. Smell, on the other hand, is 

 designed to afford us information in reference to substances 

 in a volatile or gaseous form. Invisible particles issue from 

 odorous bodies and are brought by the respired air in contact 

 with the terminal filaments of the olfactory nerve, upon which 

 an agreeable or disagreeable impression is produced. The fine- 

 ness of the particles that constitute odors is often so extreme 

 that they elude all attempts to measure or weigh them. A 

 piece of musk, for instance, may be kept for several years, 

 constantly emitting perfume without any appreciable loss o 4 ? 

 weight. In other cases, a loss of substance is perceptible, as 

 in the essential oils, which enter into the composition of the 

 ordinary perfumes. 



43. Smell, like taste, aids us in the choice of proper food, 

 leading us to reject such articles as have a rank or putrid odor, 

 and which are, as a rule, unfit to be eaten. The highest use- 

 fulness of this sense, however, consists in the protection it 

 affords to the organs of respiration. Stationed at the gateways 

 of the air-passages, it examines the current of air as it enters, 

 and warns us of. the presence of noxious gases, and of other and 

 generally invisible enemies to health. Not all dangerous vapors 

 are offensive, but almost all offensive vapors are unfit to be 

 breathed. A number of small stiff hairs grow from the margin 

 of the nostrils to prevent the entrance of dust and other atmos- 

 pheric impurities, which would be alike injurious to. the olfac- 

 tory mucous membrane and to the lungs. The benevolent 

 design of the Maker of our bodies may be observed in all parts 

 of their mechanism; but, probably, in none is it more clearly 

 displayed than in connection with the sense of smell. (Bead 

 Note 6.) 



6. The Protective Function of the Sense t)f Smell. " Smell seems 

 to be regarded as an endowment bestowed simply for pleasure, serving to 

 promote no important or vital end. That its main use is to signal danger 

 to internal parts is not duly appreciated. The detection of an offensive 

 odor is thought to be the only bad thing about it, and which, to those 

 habituated to it, is of no subsequent importance. Men even pride them- 

 selves on becoming accustomed to offensive odors, and quite enjoy the 



43. Aid given by smell ? The highest use of the sense ? Explain the mainer 



