absorbent system. Internal absorption is classified by some authors as
follows: _interstitial_, _recrementitial_, and _excrementitial_; by
others as _accidental_, _venous_, and _cutaneous_. The general cutaneous
and mucous surfaces exhale, as well as absorb; thus the skin, by means
of its sudoriferous glands, exhales moisture, and is at the same time as
before stated, a powerful absorbent. The mucous surface of the lungs is
continually throwing off carbonic acid and absorbing oxygen; and through
their surface poisons are sometimes taken into the blood. The continual
wear and waste to which living tissues are subject, makes necessary the
provision of such a system of vessels for conveying away the worn-out
materials and supplying the body with new.

* * * * *




CHAPTER VI.

PHYSICAL AND VITAL PROPERTIES OF THE BLOOD.


[Illustration: Fig. 38.
Red corpuscles of human blood, represented
at _a_, as they are seen when
rather _beyond_ the focus of the microscope;
and at _b_ as they appear when,
_within_ the focus. Magnified 400 diameters.]

[Illustration: Fig. 39.