678 TEXT-BOOK OF PHYSIOLOGY 



classification is extremely difficult. For this reason it is customary to divide 

 them into two groups: viz., agreeable and disagreeable, in accordance with 

 the feelings they excite in the individual. As the olfactory sensations give 

 rise to feelings rather than ideas, this sense plays in man a subordinate parl 

 in the acquisition of knowledge. In lower animals this sense is employed 

 for the purpose of discovering and securing food, for detecting enemies and 

 friends, and for sexual purposes. In land animals the entire olfactory appa- 

 ratus is well developed and the sense keen; in some aquatic animals, as the 

 dolphin, whale, and seal, the apparatus is poorly developed and the sense 

 dull. 



