28 DISEASES OF THE HORSE. 
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 life, 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 irregularly 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. 
