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CHAPTER XI.

PHYSIOLOGICAL ANATOMY.

EXCRETION.


The products resulting from the waste of the tissues are constantly
being poured into the blood, and, as we have seen, the blood being
everywhere full of corpuscles, which, like all living things, die and
decay, the products of their decomposition accumulate in every part of
the circulatory system. Hence, if the blood is to be kept pure, the
waste materials incessantly poured into this fluid, or generated in it,
must be as continually removed, or excreted. The principal sets of
organs concerned in effecting the separation of excrementitious
substances from the blood are the lungs, the skin, and the kidneys.

The elimination of carbonic acid through the lungs has already been
described on page 66, and the excretory function of the skin on page 70.

[Illustration: Fig. 53.
View of the kidneys, ureters, and bladder. ]

The kidneys are two bean-shaped organs, placed at the back of the