A Practical Physiology | Page 8

of
minute sacs of exceedingly delicate, structureless membrane filled with
oil. This is liquid in life, but becomes solidified after death. This tissue
is plentiful beneath the skin, in the abdominal cavity, on the surface of
the heart, around the kidneys, in the marrow of bones, and elsewhere.
Fat serves as a soft packing material. Being a poor conductor, it retains
the heat, and furnishes a store rich in carbon and hydrogen for use in
the body.
24. Adenoid or Retiform Tissue. This is a variety of connective tissue
found in the tonsils, spleen, lymphatic glands, and allied structures. It
consists of a very fine network of cells of various sizes. The tissue
combining them is known as adenoid or gland-like tissue.
[Illustration: Fig. 8.--Fibro-Cartilage Fibers. (Showing network
surrounded cartilage cells.)]
25. Cartilage. Cartilage, or gristle, is a tough but highly elastic
substance. Under the microscope cartilage is seen to consist of a matrix,
or base, in which nucleated cells abound, either singly or in groups. It
has sometimes a fine ground-glass appearance, when the cartilage is

spoken of as hyaline. In other cases the matrix is almost replaced by
white fibrous tissue. This is called white fibro-cartilage, and is found
where great strength and a certain amount of rigidity are required.
Again, there is between the cells a meshwork of yellow elastic fibers,
and this is called yellow fibro-cartilage (Fig. 8). The hyaline cartilage
forms the early state of most of the bones, and is also a permanent
coating for the articular ends of long bones. The white fibro-cartilage is
found in the disks between the bodies of the vertebrae, in the interior of
the knee joint, in the wrist and other joints, filling the cavities of the
bones, in socket joints, and in the grooves for tendons. The yellow
fibro-cartilage forms the expanded part of the ear, the epiglottis, and
other parts of the larynx.
26. General Plan of the Body. To get a clearer idea of the general plan
on which the body is constructed, let us imagine its division into
perfectly equal parts, one the right and the other the left, by a great
knife severing it through the median, or middle line in front, backward
through the spinal column, as a butcher divides an ox or a sheep into
halves for the market. In a section of the body thus planned the skull
and the spine together are shown to have formed a tube, containing the
brain and spinal cord. The other parts of the body form a second tube
(ventral) in front of the spinal or dorsal tube. The upper part of the
second tube begins with the mouth and is formed by the ribs and
breastbone. Below the chest in the abdomen, the walls of this tube
would be made up of the soft parts.
[Illustration: Fig. 9.--Diagrammatic Longitudinal Section of the Trunk
and Head. (Showing the dorsal and the ventral tubes.)
A, the cranial cavity; B, the cavity of the nose; C, the mouth; D, the
alimentary canal represented as a simple straight tube; E, the
sympathetic nervous system; F, heart; G, diaphragm; H, stomach; K,
end of spinal portion of cerebro-spinal nervous system. ]
We may say, then, that the body consists of two tubes or cavities,
separated by a bony wall, the dorsal or nervous tube, so called because
it contains the central parts of the nervous system; and the visceral or
ventral tube, as it contains the viscera, or general organs of the body, as
the alimentary canal, the heart, the lungs, the sympathetic nervous
system, and other organs.
The more detailed study of the body may now be begun by a

description of the skeleton or framework which supports the soft parts.

Experiments.
For general directions and explanations and also detailed suggestions
for performing experiments, see

Chapter XV.
Experiment 1. _To examine squamous epithelium._ With an ivory
paper-knife scrape the back of the tongue or the inside of the lips or
cheek; place the substance thus obtained upon a glass slide; cover it
with a thin cover-glass, and if necessary add a drop of water. Examine
with the microscope, and the irregularly formed epithelial cells will be
seen.
Experiment 2. _To examine ciliated epithelium._ Open a frog's mouth,
and with the back of a knife blade gently scrape a little of the
membrane from the roof of the mouth. Transfer to a glass slide, add a
drop of salt solution, and place over it a cover-glass with a hair
underneath to prevent pressure upon the cells. Examine with a
microscope under a high power. The cilia move very rapidly when
quite fresh, and are therefore not easily seen.
For additional experiments which pertain to the microscopic
examination of the elementary tissues and to other points in practical
histology,