e cells are formed of highly active protoplasm, and are busily engaged
in some sort of secretion. Such are the cells of glands,--the cells of the
salivary glands, which secrete the saliva, of the gastric glands, which
secrete the gastric juice, of the intestinal glands, and the cells of the
liver and sweat glands.

19. Connective Tissue. This is the material, made up of fibers and
cells, which serves to unite and bind together the different organs and
tissues. It forms a sort of flexible framework of the body, and so
pervades every portion that if all the other tissues were removed, we
should still have a complete representation of the bodily shape in every
part. In general, the connective tissues proper act as packing,
binding, and supporting structures. This name includes certain tissues
which to all outward appearance vary greatly, but which are properly
grouped together for the following reasons: first, they all act as
supporting structures; second, under certain conditions one may be
substituted for another; third, in some places they merge into each other.

All these tissues consist of a ground-substance, or matrix, cells, and
fibers. The ground-substance is in small amount in connective tissues
proper, and is obscured by a mass of fibers. It is best seen in hyaline
cartilage, where it has a glossy appearance. In bone it is infiltrated
with salts which give bone its hardness, and make it seem so unlike other
tissues. The cells are called connective-tissue corpuscles, cartilage
cells, and bone corpuscles, according to the tissues in which they occur.
The fibers are the white fibrous and the yellow elastic tissues.

The following varieties are usually described:

I. Connective Tissues Proper:

1. White Fibrous Tissue.
2. Yellow Elastic Tissue.
3. Areolar or Cellular Tissue.
4. Adipose or Fatty Tissue.
5. Adenoid or Retiform Tissue.

II. Cartilage (Gristle):

1. Hyaline.
2. White Fibro-cartilage.
3. Yellow Fibro-cartilage.

III. Bone and Dentine of Teeth.

20. White Fibrous Tissue. This tissue consists of bundles of very
delicate fibrils bound together by a small amount of cement substance.
Between the fibrils protoplasmic masses (connective-tissue corpuscles)
are found. These fibers may be found so interwoven as to form a sheet, as
in the periosteum of the bone, the fasciae around muscles, and the capsules
of organs; or they may be aggregated i