124 PHYSIOLOGY FOR NURSES 



which the hairlikc process is involved. Heat or cold, 

 when excessive, interferes with the acuteness of taste. 

 Smaller quantities of bitter substances can be tasted 

 than of any other, while acid, sweet, and salt each re- 

 quire larger amounts, salt the largest. Some substances 

 give different sensations on different parts of the 

 tongue, as sulphate of soda which is merely salty at the 

 tip of the tongue, but bitter at the back. Certain sub- 

 stances dissolved in the blood give rise to sensations of 

 taste. The bile in the blood in jaundice causes a bitter 

 taste, while the sugar in diabetes causes a sweet tas'.e. 



THE OLFACTORY SENSE 



The course of olfactory sensations is from the end or- 

 gans of smell in the roof and upper part of the sides of 

 each nostril, along the olfactory nerves to the bulb and 

 thence to the base of the brain at the lower and inner 

 part of the temporosphenoidal lobe just in front of the 

 center for taste. 



The smell sense is one of the oldest in the history of 

 life. When highly developed it was not only of great 

 defensive strength in enabling its possessor to detect 

 the presence of enemies, but was of equal offensive serv- 

 ice in the pursuit of prey. In man it has dwindled to 

 such an extent that he vaguely defines odors as pleas- 

 ant or disagreeable, while a dog can still detect the 

 odor, of a man, imperceptible usually to himself and as- 

 sociates, and follow him unerringly after hours have 

 elapsed and pick him out of a crowd of others. 



The substances which arouse, or stimulate, the sense 

 of smell, give off inappreciable particles, probably gas- 

 eous in form, which are carried by inhaled air to the 

 end organs of the olfactory nerve, are there dissolved 

 by the moisture present and chemically stimulate the 



