DISEASES OF THE HOUSE. 483 



dense. These fibers once created require the constant presence of 

 ihiids around them in order to retain their functional condition, as a 

 piece of harness leather demands continual oiling to keep its strength, 

 l)ut they undergo no change or alteration in their form until destroyed 

 ])y death. 



{(■) Cells, which may even be regarded as low forms of life, are 

 masses of protoplasm or amorphous living matter, with a nucleus and 

 frequently a nucleolus, Avhich are capable of assimilating nutriment or 

 food, propagating themselves either into others of the same form or 

 into lixed cells of another outward appearance and different fum^tion 

 but of the same constitution. It is simplj^ in the mode of grouping 

 of these elements that we have the variation in tissues, as (1) loose 

 connective tissue, (2) aponeurosis and tendons, (3) muscles, (4) carti- 

 lage, (5) bones, (6) epithelia and endothelia, (7) nerves. 



(1) Loose connective tissue forms the great framework, or scaffolding, 

 of the body, and is found under the skin, between the muscles sur- 

 rounding the bones and blood vessels, and entering into the structures 

 of almost all of the organs. In this the fibers are loosely meshed 

 together like a sponge, leaving spaces in which the nutrient fluid and 

 cells are irregularly distributed. This tissue we find in the skin, in 

 the spaces between the organs of the body where fat accumulates, and 

 as the framework of all glands. 



(2) Aponeurosis and tendons are structures which serve for the ter- 

 mination of muscles and for their contention, and for the attachment 

 of bones together. In these the fibers are more frequent and dense, 

 and are arranged with regularit}', cither crossing each other or hnng 

 parallel, and here the cells are found in minimum quantity. 



(3) Muscles. — In these the cells lie end to end, forming long fibers 

 which have the power of contraction, and the connective tissue is in 

 small quantity, serving the passive purpose of a band around the con- 

 tractile elements. 



(4) In cartilage a mass of firm amorphous substance, with no vas- 

 cularity and little vitality, forms the bed for the chondroplasts, or 

 cells of this tissue. 



(.")) Bone differs from the above in having the amorphous matter 

 impregnated with lime salts, which gives it its rigidity and firnmcss. 



(6) Epithelia and endothelia, or the membranes which cover the 

 body and line all of its cavities and glands, are made up of single or 

 stratified and multiple layers of cells bound together by a glue of 

 amorphous substance and resting on a \a,jer composed of fibers. 

 When the membrane serves for secreting or excreting purposes, as 

 in the salivar}^ glands or the kidneys, it is usually simple; when it 

 serves the mechanical purpose of protecting a part, as over the 

 tongue or skin, it is invariably multiple and stratified, the surface 

 wearing away while new cells replace it from beneath. 



