The principal saline substances are common salt, the sulphates and
phosphates of potassium, sodium, calcium, and magnesium. In addition to
the animal and the saline matters, the urine also contains a small
quantity of carbonic acid, oxygen and nitrogen.

* * * * *




CHAPTER XII.

PHYSIOLOGICAL ANATOMY.

THE NERVOUS SYSTEM.


Hitherto, we have only considered the anatomy and functions of the
organs employed in Digestion, Absorption, Circulation, Respiration,
Secretion and Excretion. We have found the vital process of nutrition to
be, in all its essential features, a result of physical and chemical
forces; in each instance we have presupposed the existence and activity
of the nerves. There is not an inch of bodily tissue into which their
delicate filaments do not penetrate, and form a multitude of conductors,
over which are sent the impulses of motion and sensation.

[Illustration: Fig. 54.
The Nervous System.]

Two elements, _nerve-fibers_ and _ganglionic corpuscles_, enter into the