28 DISEASES OF THE HOESE. 



kinds — white connective tissue fibers, only slightly extensible, pliable, 

 and very strong, and yellow elastic fibers, elastic, curly, ramified, and 

 very dense. These fibers once created require the constant presence 

 of fluids around them in order to retain their functional condition, as 

 a piece of harness leather demands continual oiling to keep its 

 strength, but they undergo no change or alteration in their form 

 until destroyed by death. 



(c) Cells, which may even be regarded as low forms of lifej are 

 masses of protoplasm or amorphous living matter, with a nucleus 

 and frequently a nucleolus, which are capable of assimilating nutri- 

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

 form or into fixed cells of another outward appearance and differ- 

 ent function but of the same constitution. It is simply in the mode 

 of the grouping of these elements that we have the variation in tis- 

 sues, as (1) loose connective tissue, (2) aponeurosis and tendons, 

 (3) muscles, (4) cartilage, (5) bones, (6) epithelia and endothelia, 

 (7) nerves. 



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

 folding, of the body, and is found under the skin, between the 

 muscles surrounding the bones and blood vessels, and entering into 

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

 meshed together like a sponge, leaving spaces in which the nutrient 

 fluid and cells are irregiTlarly distributed. This tissue we find in the 

 skin, in the spaces between the organs of the body where fat accumu- 

 lates, and as the framework of all glands. 



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

 termination of muscles and for their contention, and for the attach- 

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

 dense, and are arranged with regularity, either crossing each other or 

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



(3) In the muscles 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. 



(5) Bone differs from the above in having the amorphous matter 

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



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

 body and line all 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 layer composed of fibers. 



