SENSE OF SMELL. 553 



which the finest chemical tests fail to appreciate. Thus Valentin 

 has estimated that the two-millionths of a milligram of musk is 

 sufficient to excite the specific energy of a man's olfactory appa- 

 ratus. 



No satisfactory classification of odors has been made out. The 

 common division into agreeable and disagreeable smells, or scents 

 and stinks, is dissimilar in different individuals, and therefore 

 cannot have a physiological basis. 



With smell, as with taste, no degree of intensity of stimulation 

 can be said to produce pain, though disgust, nausea, vomiting, 

 and many other psychical and nervous operations may be induced 

 by various smells, and the appetites are either excited or annulled 

 by different excitations of the olfactory nerves. 



