THE SPECIAL SENSES. 195 



The fineness 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 sev- 

 eral years, constantly emitting perfume, without any ap- 

 preciable loss of weight. In other cases, a loss of substance 

 is perceptible, such as 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 usefulness of this sense, however, consists in 

 the protection it affords to the organs of respiration. Sta- 

 tioned 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 ene- 

 mies 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 at- 

 mospheric impurities, which would be alike injurious to the 

 olfactory mucous membrane and to the lungs. The benev- 

 olent 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. 



44. The sense of smell is developed in a remarkable de- 

 gree in certain of the inferior animals, and is especially 

 acute in reference to the peculiar emanations that appear 

 to characterize the different animals. The lion and other 

 carnivorous beasts scent their prey from a great distance; 

 and the fox-hound is able to track the fox through thickets 

 and over open country for many miles; while the timid, 

 helpless herbivora, such as the deer and sheep, find in the 



43. Aid given by ymell? The highest use of the sense? Explain the manner. 



44. Sense of smell in the inferior animals? How, and in what cases, illus- 

 trated ? 



