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OF THE ORGANIC SYSTEM. 93
separation of various matters from the blood, and the
additions to the blood must exactly correspond with
these, to keep up the equilibrium of life. After arriv
ing at his full growth, a man may live on for many
years, scarcely ever varying in his weight. Yet he
consumes tons of food, and gives off tons of excretions.
There may be a gradual deposition of fatty matter in
the cells of the areolar tissue, a stock of food laid up for
the wants of age, when the partial failure of digestion
may render such a supply convenient ; but this vari
ation is but slight in ordinary cases. Day by day
consumption and waste very nearly balance each other.
The reader may have already perceived that there
into the blood,
are two modes by which matters get
and they get out of it in a similar manner. One mode
is by simple mechanical absorption or transudation;
the other is a more vital process, and is performed by
means of glands, or cells, under the influence of organic
of water is taken into
nerves. For example, if a pint
the stomach, when demanded by thirst, it is sucked up
by the veins as by a sponge. In a feverish state of the
system, if a pint of water is injected into the rectum, it
is also quickly absorbed into the circulation. The
veins of the skin also absorb water l-apidly in bathing,
and even from the atmosphere. Water is not digest
ed, but is itself the great digestive agent. It undergoes
no change, unless by analysis and synthesis, but is sim
ply absorbed. This is also the fact respecting many
substances dissolved in water, or themselves liquid ;
and this is the reason why water for drinking should be
soft and pure. Alcohol passes from the stomach di
rectly into the circulation, as alcohol by venous absorp-