communication between the cells is still more remarkable
in regard to air. Sometimes, when an accidental opening has been made
from the air-cells of the lungs into the contiguous cellular tissue,
the air in respiration has penetrated every part until the whole body
is so inflated as to occasion suffocation. Butchers often avail
themselves of the knowledge of this fact, and inflate their meat to
give it a fat appearance.

31. "Although this tissue enters into the composition of all organs,
it never loses its own structure, nor participates in the functions of
the organ of which it forms a part. Though present in the nerves, it
does not share in their sensibility; and though it accompanies every
muscle and every muscular fibre, it does not partake of the
irritability which belongs to these organs."

32. Several varieties of tissue are formed from the cellular; as, the
_Se'rous_, _Der'moid_, _Fi'brous_, and several others.

33. The SEROUS TISSUE lines all the closed, or sac-like cavities of
the body; as, the chest, joints, and abdomen. It not only lines these
cavities, but is reflected, and invests the organs contained in them.
The liver and the lungs are thus invested. This membrane is of a
whitish color, and smooth on its free surfaces. These surfaces are
kept moist, and prevented from adhering by a _se'rous_ fluid, which is
separated from the blood. The use of this membrane is to separate
organs and also to facilitate the movement of one part upon another,
by means of its moist, polished surfaces.

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Give observation 2d. 31. What is said of the identity of this tissue?
32. Name the varieties of tissue formed from the cellular. 33. Where
is the serous tissue found? What two offices does it perform? Give its
structure. What is the use of this membrane?

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34. The DERMOID TISSUE covers the outside of the body. It is called
the _cu'tis_, (skin.) This membrane is continuous with the mucous at
the various orifices of the body, and in these situations, from the
similarity of their structure, it is difficult to distinguish between
them.

_Observations._ 1st. In consequence of the continuity and similarity
of structure, there is close sympathy between the mucous and dermoid
membranes. If the functions of the skin are disturbed, as by a chill,
it will frequently cause a catarrh, (cold,) or diarrhoea. Again, in
consequence of this intimate sympathy, these complaints can