A YEAR IN SCIENCE 135 



mucous membrane lining the upper part of the cavity 

 of the nose. Particles of matter in the form of a gas 

 striking this membrane stimulate the nerves of smell, 

 olfactory nerves. To determine which of the sub- 

 stances named under "Apparatus" have taste and 

 Avhich have odor, perform the following experiment. 

 Place each of these substances 011 the tongue of a 

 pupil who has been previously blindfolded, and who is 

 holding his nose tightly. Record the substance recog- 

 nized by taste alone. Repeat, leaving the nose free. 

 Record the substances recognized by smell alone; by 

 taste and smell combined. 



Exercise 91. Organ of Sight. 



Object: To study the structure and action of the 

 eye. 



Apparatus 



Model of human eye Lenses 



Directions: A. With the aid of a mirror examine 

 the eye. Feel the upper eyelid; fold it. In what part 

 of it is there a stiff, thick strip of connective tissue? 

 Compare with this the corresponding strip in the 

 lower lid. At the angle of the lower lid, about one- 

 eighth of an inch from the inner corner, look for a 

 little papilla in which is the opening of the tear duct. 

 Can you find a similar opening in the upper lid? 

 Notice the eyeball. What do you find in the inner 

 corner which is different from the outer? The eye 



