If
the living element be altered by disease, then it loses its power of
specific attraction.

I do not regard the blood as the cause of chronic dyscrasiae; for I do
not regard the blood as a permanent tissue independently regenerating
and propagating itself, but as a fluid in a state of constant dependence
upon other parts. I consider that every dyscrasia _is dependent upon a
permanent supply of noxious ingredients from certain sources_. As a
continual ingestion of injurious food is capable of vitiating the blood,
in like manner persistent disease in a definite organ is able to furnish
the blood with a continual supply of morbid materials.

The essential point, therefore, is to search for the _local sources_ of
the different dyscrasiae which cause disorders of the blood, for every
permanent change which takes place in the condition of the circulating
juices must be derived from definite organs or tissues.

The blood contains certain morphological elements. It contains a
substance, _fibrine_, which appears as fibrillac when the blood clots,
and red and colourless blood corpuscles.

The red blood corpuscles contain no nuclei except at certain periods of
the development of the embyro. They are lighter or darker red according
to the oxygen they contain. When treated with concentrated fluids they
shrivel; when treated with diluted fluids they swell. They are rather
coin-shaped, and when a drop of blood is quiet they are usually found
aggregated in rows, like rouleaux of money.

The colourless corpuscles are much less numerous than the red
corpuscles--only one to 300--but they are larger, and contain nuclei.
When blood coagulates the white corpuscles sink more slowly and appear
as a lighter coloured layer on the top of the clot.

Pus cells are very like colourless corpuscles, and the relation between
the two has been much debated. A pus cell can be distinguished from a
colourless blood cell only by its mode of origin. If it have an origin
external to the blood, it must be pus; if it originate in the blood, it
must be considered to be a blood cell.

In the early stages of its development, a white blood corpuscle is seen
to modify by division; but in fully-developed blood such division is
never seen. It is probable that colourless white corpuscles are given to
the adult blood by the lymphatic glands. Every irritation of a part
which is freely connected with lymphatic glands increases the number of
colourless cells in th