A Practical Physiology | Page 4

the most
important inorganic salts the body contains. It is absolutely necessary
for continued existence. By a combination of phosphorus with sodium,
potassium, calcium, and magnesium, the various phosphates are
formed.
The phosphates of lime and soda are the most abundant of the salts of
the body. They form more than half the material of the bones, are found
in the teeth and in other solids and in the fluids of the body. The special
place of iron is in the coloring matter of the blood. Its various salts are
traced in the ash of bones, in muscles, and in many other tissues and
fluids. These compounds, forming salts or mineral matters that exist in
the body, are estimated to amount to about 6 per cent of the entire
weight.
9. Organic Compounds. Besides the inorganic materials, there exists in
the human body a series of compound substances formed of the union
of the elements just described, but which require the agency of living
structures. They are built up from the elements by plants, and are called
organic. Human beings and the lower animals take the organized
materials they require, and build them up in their own bodies into still

more highly organized forms.
The organic compounds found in the body are usually divided into
three great classes:
1. Proteids, or albuminous substances. 2. Carbohydrates (starches,
sugars, and gums). 3. Fats.
The extent to which these three great classes of organic materials of the
body exist in the animal and vegetable kingdoms, and are utilized for
the food of man, will be discussed in the chapter on food (

Chapter V.
). The Proteids, because they contain the element nitrogen and the
others do not, are frequently called nitrogenous, and the other two are
known as non-nitrogenous substances. The proteids, the type of which
is egg albumen, or the white of egg, are found in muscle and nerve, in
glands, in blood, and in nearly all the fluids of the body. A human body
is estimated to yield on an average about 18 per cent of albuminous
substances. In the succeeding chapters we shall have occasion to refer
to various and allied forms of proteids as they exist in muscle (myosin),
coagulated blood (fibrin), and bones (gelatin).
The Carbohydrates are formed of carbon, hydrogen, and oxygen, the
last two in the proportion to form water. Thus we have animal starch,
or glycogen, stored up in the liver. Sugar, as grape sugar, is also found
in the liver. The body of an average man contains about 10 per cent of
Fats. These are formed of carbon, hydrogen, and oxygen, in which the
latter two are not in the proportion to form water. The fat of the body
consists of a mixture which is liquid at the ordinary temperature.
Now it must not for one moment be supposed that the various chemical
elements, as the proteids, the salts, the fats, etc., exist in the body in a
condition to be easily separated one from another. Thus a piece of
muscle contains all the various organic compounds just mentioned, but
they are combined, and in different cases the amount will vary. Again,
fat may exist in the muscles even though it is not visible to the naked
eye, and a microscope is required to show the minute fat cells.
10. Protoplasm. The ultimate elements of which the body is composed
consist of "masses of living matter," microscopic in size, of a material
commonly called protoplasm.[2] In its simplest form protoplasm

appears to be a homogeneous, structureless material, somewhat
resembling the raw white of an egg. It is a mixture of several chemical
substances and differs in appearance and composition in different parts
of the body.
Protoplasm has the power of appropriating nutrient material, of
dividing and subdividing, so as to form new masses like itself. When
not built into a tissue, it has the power of changing its shape and of
moving from place to place, by means of the delicate processes which it
puts forth. Now, while there are found in the lowest realm of animal
life, organisms like the amoeba of stagnant pools, consisting of nothing
more than minute masses of protoplasm, there are others like them
which possess a small central body called a nucleus. This is known as
nucleated protoplasm.
[Illustration: Fig. 1.--Diagram of a Cell.
A, nucleus; B, nucleolus; C, protoplasm. (Highly magnified) ]
11. Cells. When we carry back the analysis of an organized body as far
as we can, we find every part of it made up of masses of nucleated
protoplasm of various sizes and shapes. In all essential features these
masses conform to the type of protoplasmic matter just described. Such
bodies are called cells. In many cells the nucleus is finely granular or
reticulated