interior of the body. In some animals circulation is not distinct from
digestion, in others respiration and digestion are performed by the same
organs; but as we rise in the scale of animal life, digestion and
circulation are accomplished in separate cavities, and the functions of
nutrition become more complex and distinct.


* * * * *




CHAPTER V.

PHYSIOLOGICAL ANATOMY.

ABSORPTION.


[Illustration: Fig. 35.
Villi of the small intestine greatly magnified.]

_Absorption_ is the vital function by which nutritive materials are
selected and imbibed for the sustenance of the body. Absorption, like
all other functional processes, employs agents to effect its purposes,
and the _villi_ of the small intestine, with their numberless projecting
organs, are specially employed to imbibe fluid substances; this they do
with a celerity commensurate to the importance and extent of their
duties. They are little vascular prominences of the mucous membrane,
arising from the interior surface of the small intestine. Each villus