INTRODUCTION 



II 



a covering for the surface of the body, and the essential part 

 of various organs called glands. 



There are several varieties of this tissue. Thus, we 

 have the flat cells of the outer skin and the lining of the 

 mouth, the pear-shaped cells in the 

 lining of the stomach and the intes- 

 tines, and cells with fine, threadlike 

 fringes, called cilia, found in the lining 

 of the air passages (Sec. 225). 



Experiment 2. To examine one form of 

 epithelium (squamous}. Gently scrape the 

 inside of the lips or cheek with an ivory 

 paper knife. Place a tiny portion of the 

 substance thus obtained upon a glass slide. 

 Cover it with a thin' cover glass, and if neces- 

 sary add a drop of water. Examine with 

 the microscope, and the irregularly formed 

 (squamous, or pavement) epithelial cells 

 may be seen. 



Experiment 3. To examine another form 

 of epithelium (ciliated}. With the back of 

 a knife blade gently scrape a little of the FIG. 5. 

 membrane from the roof of a frog's mouth. 

 Transfer to a glass slide and add a drop of 

 salt solution. Place over it a cover glass 



with a hair underneath to prevent pressure upon the cells. Examine 

 with a microscope under a high power. The cilia move quite rapidly 

 while they are fresh (Sec. 225). 



Cross-Section of 

 Epithelium from the 

 CEsophagus. 



19. The Connective Tissues. Just as certain cells develop 

 into masses of cells which we call muscle, brain, and skin, 

 so other cells are set apart to produce tissues by which 

 the frame of the body and its organs are molded and held 

 together. They are called connective tissues. They form a 



