stage of progress. While the most highly trained and the best furnished
intellect may find all its resources insufficient, when it strives to
reach the heights and penetrate into the depths of the problems of
physiology, the elementary and fundamental truths can be made clear to
a child.

No one can have any difficulty in comprehending the mechanism of
circulation or respiration; or the general mode of operation of the
organ of vision; though the unravelling of all the minutiae of these
processes, may, for the present, baffle the conjoined attacks of the
most accomplished physicists, chemists, and mathematicians. To know the
anatomy of the human body, with even an approximation to thoroughness,
is the work of a life; but as much as is needed for a sound
comprehension of elementary physiological truths, may be learned in a
week.

A knowledge of the elements of physiology is not only easy of
acquirement, but it may be made a real and practical acquaintance with
the facts, as far as it goes. The subject of study is always at hand,
in one's self. The principal constituents of the skeleton, and the
changes of form of contracting muscles, may be felt through one's own
skin. The beating of one's heart, and its connection with the pulse,
may be noted; the influence of the valves of one's own veins may be
shown; the movements of respiration may be observed; while the
wonderful phenomena of sensation afford an endless field for curious
and interesting self-study. The prick of a needle will yield, in a drop
of one's own blood, material for microscopic observation of phenomena
which lie at the foundation of all biological conceptions; and a cold,
with its concomitant coughing and sneezing, may prove the sweet uses of
adversity by helping one to a clear conception of what is meant by