14 APPLIED PHYSIOLOGY 



9. Tissues. While each cell eats, grows, and pro- 

 duces other cells more or less independently of the rest, 

 yet, like the members of a large family, each works for 

 the benefit of all the others, and, in turn, is dependent 

 upon them for things which it cannot do so well as they. 

 Cells doing special kinds of work are collected in orderly 

 groups called tissues. Six kinds of tissues are well 

 marked, 



(1) Muscular Tissue. Groups of ribbonlike cells which 

 have the power of^ moving the adjacent parts are found 

 everywhere in the body, and form muscular tissue. This 

 tissue is usually as abundant as all the rest of the tissues 

 taken together. 



(2) Epithelial Tissue. Covering all the surface of the 

 body, and lining every cavity and tube which connects 

 with the surface of the body, is a layer of firm cells which 

 form epithelial tissue. It protects the underlying parts 

 and manufactures all the various fluids of the body. 

 From it, also, the hair and nails are produced. Epithelial 

 tissue is abundant and important. 



(3) Nervous Tissue. There are cells which control all 

 the others. By means of their long, threadlike prolonga- 

 tions they convey orders to every cell in the body. They 

 and their prolongations form nervous tissue. 



(4) Connective Tissue. Surrounding each cell, and 

 holding it in place, are the extremely fine arms of small 

 cells called connective tissue (szt p. 11). Its amount varies 

 greatly in different parts of the body and in different per- 

 sons, but its total amount is always very large. In some 

 parts of the body, as in the skin and lungs, there is a 

 special kind of connective tissue which is very elastic, and 

 gives to the parts their stretching properties. This tissue 

 is called "yellow elastic tissue" from its color. 



