SMELL. 333 



Back of hand 1.23 inches 



Forearm 158 " 



Sternum 1.76 " 



Back of neck 2.11 " 



Middle of back 2. 64 



The Temperature Senses. By these is meant our faculty 

 of perceiving cold and warmth; and, with the help of these 

 sensations, of perceiving temperature differences in external 

 objects. The organs are the skin, the mucous mem- 

 brane of mouth, pharynx, and gullet, and of the entry of 

 the nose. Burning the skin will cause pain, but not a true 

 temperature sensation, which is quite as different from 

 pain as is touch. 



Smell. The olfactory organ consists of the mucous 

 membrane of the upper parts of the nasal cavities; in it the 

 endings of the olfactory nerves are spread. It covers the 

 upper and lower turbinate bones (o, p, Fig. 41) (which are 

 expansions of the ethmoid on the outer wall of the nostril- 

 chamber), the opposite part of the partition between -the 

 nares, and that part of the roof of the nose (n, Fig. 41) 

 which separates it from the cranial cavity. 



Odorous Substances, the stimuli of the olfactory apparatus, 

 are always gaseous. They frequently act powerfully when 

 present in very small quantity. A grain or two of musk 

 kept in a room will give the air in it an odor for years, and 

 yet at the end will hardly have diminished in weight, so 

 infinitesimal is the quantity given off from it to the air 

 and able to excite the sense of smell. While some gases or 



What is the temperature sense? What are its organs? 



Of what does the olfactory organ consist? 



In what point do all odorous substances agree? Illustrate the 

 efficiency, so far as producing smell sensations is concerned, of a 

 very small quantity of an odorous substance. Do all gases stimulate 

 the olfactory apparatus? 



