CHAPTER IX. 
ELEMENTARY PHYSIOLOGY. 
The body is made up of various parts or organs, each with a 
separate action or function. 
Organs again are composed of certain definite structures or 
tissues differing widely from one another, not only in their physical 
characters and appearance but also in their functions. 
All tissues are composed of certain similar elements more or 
less modified, which are called cells, and the functions of the different 
tissues are due to the activities of their cells. 
The cell is a minute mass of living substance or protoplasm, in 
which is situated a more or less well-defined body, the nucleus. 
These are the essential parts of a cell. Each little cell possesses 
the power of assimilating particles of food brought to it, of movement 
and of reproduction. 
From the protoplasm of the cells the various tissues of the body 
bone, muscle, nerve, etc. — are formed. The animal body is originally 
a single cell, and from this, by division, a mass of simple cells is 
produced, which become arranged in the embryo into three layers 
an outer, a middle and an inner — and from these three layers the 
different sets of tissues develop. 
Tissues are divided into two classes : — 
[a) The vegetative tissues which support, bind together, 
protect and nourish the body : as examples of such 
tissues we have bone tissue, fibrous tissue of ligaments 
and tendons, skin and gland tissue. 
(d) The master tissues of the body, muscle and nerve. 
A detailed description of these tissues is unnecessary here; it 
will only be observed, however, for the benefit of the lay reader 
that there are two kinds of muscle tissue : one under the control of 
the will and therefore called voluntary muscle, and the other 
not so controlled and known as involuntary muscle, such as 
for instance, the muscles of the intestine. Voluntary muscles are 
actuated by nerve impulses from the central nervous system. 
Nerves pass from the skin and various tissues inwards towards the 
brain, carrying impressions to that organ, and from the brain nerves 
pass outwards to the muscles and tissues, stimulating them to 
action. The brain itself is nothing more than a collection of nerve: 
