THE RESPIRATORY ORGANS 181 



the lungs and the other side with the walls of the thorax. 

 Between the two would be the space that really is the cavity 

 of the bag. When the lungs move, these two layers of the sac 

 glide over each other. The layers themselves are made of 

 glandular cells which secrete a clear, watery liquid into the 

 space between them, keeping their surfaces moist and mak- 

 ing it possible for the lungs to move without friction or irrita- 

 tion. 



DISEASES OF THE RESPIRATORY ORGANS 



Colds. The commonest ailment of the respiratory organs 

 is what is called a cold. This is primarily an inflammation of 

 the mucous membrane of the nose and throat. By the term 

 inflammation is meant an enlargement of the capillary blood 

 vessels, causing too abundant a supply of blood in the region 

 in question and bringing about a variety of other undesirable 

 effects, such as great sensitiveness, pain and, perhaps, fever. 

 In an ordinary cold the mucous membrane is very sensitive, 

 secretes an abundance of mucus and becomes swollen. This 

 state of things may interfere with the free passage of air, 

 since the nostrils may be so closed by the swollen membranes 

 that one can breathe only through the mouth. Soaking the 

 feet in hot water and drinking hot lemonade will sometimes 

 prevent the development of a cold and is usually effective 

 in the initial stages. 



Taking Cold. Perhaps there is no way of avoiding colds 

 entirely, but it is possible to reduce their frequency. Oddly 

 enough, the method which most people adopt to prevent colds 

 frequently results in making them more, rather than less 

 susceptible to this ailment. To understand this seeming 

 paradox, we should find out first, what causes lead up to 

 a cold. The actual cause of colds is not known though they are 

 perhaps due to bacteria. It is quite certain that they are not 

 induced simply by exposure to cold, as the name would lead 

 one to believe, but are associated with the imperfect control 



