40 THE MUCOUS MEMBRANE AND SKIN. 
How do gland cells in a state of activity differ from those in a state 
of rest ? 
A gland-cell while in a condition of rest becomes filled with the 
material for secretion, which usually gives the cell a granular appear- 
ance. During the stage of activity the material which has accumu- 
lated in the cell is discharged. The cell becomes clear, or may be 
broken up in the process. 
THE MUCOUS MEMBRANE AND SKIN. 
MUCOUS MEMBRANE. 
Where are the mucous membranes situated ? 
They are found lining all passages and cavities of the body, which 
communicate with the exterior. 
What are the two main divisions of mucous membrane ? 
The gastro-pneumonic membrane, beginning at the lips, lining the 
mouth, trachea and lungs, the csophagus and entire alimentary 
tract to the rectum, where it meets the skin again. The genito-urinary 
membrane, beginning at the meatus urinarius and investing not only 
the entire urinary tract of both sexes, but also lining the organs of 
generation. 
What are the physical properties of mucous membranes ? 
They are nearly opaque and are easily torn on account of the small 
amount of tenacity and elasticity possessed by them. 
What is the structure of mucous membrane in general ? 
The surface is covered with epithelium, which, when stripped of, 
leaves the corium as in true skin. 
What are the different varieties of cells covering mucous mem- 
branes ? 
They may be scaly and stratified or columnar or ciliated. 
What portions of a mucous membrane are concerned in producing 
its proper secretion ? 
When the surface is composed of stratified epithelium the mucus is 
secreted by glands in the membrane lined with cylindrical or polyhedral- 
shaped cells. When the surface is made up of a layer of cylindrical 
or ciliated epithelium the mucus is secreted by cells in this same layer, 
and the glands in the mucous membrane are devoted to the secretion 
of some special product. 
