218 THE STRUGGLE FOR LIFE. 
the chemical and other compounds, such as the bile and 
gastric juice, essential to digestion and to other purposes. 
In this way, also, the secretions of the glandular cells are 
essential to the health of the other cells of the body. 
I next come the red Blood-corpuscles. These are round 
in outline, slightly concave on each side, and of so uniform 
a diameter, viz: one three thousand two hundredths of an 
inch, that they are frequently used as a measure of the size 
of other microscopic objects. Their principal function is to 
carry Oxygen from the external air to the cells of the 
body, and when their number falls much below four millions 
in a cubic centimetre, the whole body suffers and the 
person becomes anaemic. 
The third element is the white cells. These are true 
cells, provided with a nucleus, -have a granular appearance, 
and are a little larger than the red disks. I have already 
said that they are much fewer in number than the others, 
and of their function I shall speak presently. 
If we examine through the microscope the blood as it 
flows through a living capillary, we observe that it always 
flows in one direction, and that the red disks pass im a 
rapid stream along the centre of the vessel, while outside, 
or rather, around them is a layer of transparent plasma, in 
this the white cells are carried along more slowly. The 
white cells may be looked upon as policemen, always on 
the watch to protect the body from its enemies, introduced 
from without, such as Bacteria, or from erring portions of 
the body itself, but I shall explain this more fully later on. 
When the body is in a state of perfect health, every cell 
is not only furnished with sufficient food for its nourish- 
ment, but its waste products are also completely removed, 
and interference with either of these conditions produces 
disease. It follows from this, that if any part or organ 
appropriates an undue proportion of the available nourish- 
ment, other parts and organs must necessarily suffer from 
