readily changed
into the other. There is no fluid that does not contain solid matter
in solution, and no solid matter that is destitute of fluid.

18. In different individuals, and at different periods of life the
proportion of fluids and solids varies. In youth, the fluids are more
abundant than in advanced life. For this reason, the limbs in
childhood are soft and round, while in old age they assume a hard and
wrinkled appearance.

19. The fluids not only contain the materials from which every part of
the body is formed, but they are the medium for conveying the waste,
decayed particles of matter from the system. They have various names,
according to their nature and function; as, the blood, and the bile.

20. The solids are formed from the fluids, and consequently they are
reduced, by chemical analysis, to the same ultimate elements. The
particles of matter in solids are arranged variously; sometimes in
_fi'bres_, (threads,) sometimes in _lam'i-nae_, (plates,) sometimes
homogeneously, as in basement membranes. (Appendix A.)

21. The parts of the body are arranged into _Fi'bres_, _Fas-cic'u-li_,
_Tis'sues_, _Or'gans_, _Ap-pa-ra'tus-es_, and _Sys'tems_.

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17. What substances enter into the structure of the human body? Are
they essentially the same? 18. What is said of these substances at
different periods of life? 19. What offices do the fluids of the
system perform? 20. What is said of the solids? How are the particles
of matter arranged in solids? 21. Give an arrangement of the parts of
the body.

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22. A FIBRE is a thread of exceeding fineness. It is either
cylindriform or flattened.

23. A FASCICULUS is the term applied to several fibres united. Its
general characteristics are the same as fibres.

24. A TISSUE is a term applied to several different solids of the
body.

25. An ORGAN is composed of tissues so arranged as to form an
instrument designed for action. The action of an organ is called its
_function_, or use.

_Example._ The liver is an organ, and the secretion of the bile from
the blood is one of its functions.[1]

[1] Where examples and observations are given or experiments
suggested, let the pupil mention other analogous ones.

26. An APPARATUS is an assemblage of organs designed to produce
certain results.

_Example._ The digestive apparatus consists of the teeth, stomach,
liver, &c., all of which aid in the digestion of