422
THE MUCOUS MEMBRANES.
during life, for one part of the heart is always distended with blood,
while the other part is contracted; and even if a vacuum could be
produced in the pericardium by the contraction of one part of the
heart, it would be immediately occupied by the lungs, expanded by
the external air entering through the bronchi.
There subsists between the different serous sqcs such a sympathetic
connection, that inflammation in one is readily communicated to the
others. They become vascular by inflammation. A disease peculiar
to them is the effusion of the serum of the blood, and it frequently
occurs when the viscera invested by them are the seat of organic
disease. The fluid effused into the large serous cavities, frequently
contains not merely the components of true serum of the blood, but
also fibrin in solution, as is shown by its spontaneous coagulation to
a jelly-like mass, which afterwards separates into a clot of small size,
and a limpid fluid. In consequence of this coagulation of the fibrin
not taking place generally until after the lapse of several hours, it has
been, until recently, seldom observed.
The mucous membranes line all those passages by which internal
parts communicate with the exterior, and by which either matters
are eliminated from the body or foreign substances taken into it.
They are soft and velvety, and extremely vascular. In their chemi¬
cal properties they appear to differ essentially from the skin; for they
yield no gelatin by boiling, are wholly insoluble in water, and even
by long continued boiling are merely rendered hard and brittle.
Their basis, or proper texture, would seem therefore to belong to the
albuminous structures, (page 115.) Their internal or free surface is
covered with epithelium, the structure of which has been described
at page 108. The external surface of the mucous membranes is
attached to various other tissues: in the tongue, for example, to
muscle; on cartilaginous parts, to perichondrium; in the cells of the
ethmoid bone, in the frontal and sphenoid sinuses, as well as in the
tympanum, to periosteum; in the intestinal canal it is connected with
a firm membrane or fascia, (the tunica propria of the intestines,)
which on its exterior also gives attachment to the muscular fibres of
the third coat of the intestines.
The mucous membranes may be distinguished into several princi¬
pal tracts:—1. The mucous membrane of the nose, from which pro¬
longations are sent into the sinuses communicating with the nostrils;
and which, through the medium of the lachrymal canal and puncta,
is continuous with the conjunctiva of the eye and eyelids. The con¬
junctiva is as certainly a mucous membrane as any other of which
the character has not been doubted. It participates in the diseases
of the mucous membranes, as well the chronic blennorrhœa as the
catarrhal affections; and in every case of violent catarrh of the mu¬
cous membrane of the nose, the conjunctiva is affected in both stages
of the disease. It has nothing in common with the serous mem¬
branes, either in its secretion,—for the limpid secretion of the eyes is
derived from the lachrymal gland,—or in its form, which is not that
of a closed sac.
2. The mucous membrane of the mouth. This mucous tract com¬
municates in the throat with that of the nose, and sends a prolonga-