2. _The lymphoid tissue_: The lymph is another of the life-giving
liquids of the body, which through a vascular system of its own, draws
certain nutritive substances from the food and carries them to certain
organs which it feeds, especially the nerves.

After this slow task is completed, the rest of the lymph enters the
blood and is carried by it to other parts of the body where only smaller
quantities of lymph are needed for nourishing purposes.

The proper quality and chemical composition of the lymph, which is
different from that of the blood, is of no less importance than that of
the plasma for the preservation and regeneration of the organism.

What the plasma is to the blood, the lymph is to the nerves.

3. _The nerve tissue_: A particular aggregation of cells forms the
nerves, which, emanating from their center in the brain and spine, run
as another separate system all through the body.

This system, however, is not one of vessels; but the nerves may best be
compared to the wires of a telephone system, establishing connection
between the remotest parts of the body and its central point, from which
the directions for both voluntary and involuntary movement are given and
transmitted through the nerves.

They are of a peculiar chemical composition in which the nerve fat
(lecithin) plays a very important part, since its frequent presence in
insufficient quantity is among the most common causes of a great number
of nervous and other diseases.