504 
application in accordance with that necessity 
for precision of thought and expression which 
characterizes modern science. The exposition 
contained in the article Mucus will render it 
superfluous for me to define its present accept- 
ation. It is denied by Dr. Gruby that the 
viscid form of mucus is a normal secretion 
from any membrane whatever, and he considers 
its existence as a certain mark of diseased ac- 
tion. This view, if less absolute, would be in 
@ great measure correct, since there is no doubt 
that in a state of perfect health most mucous 
surfaces are wholly unprovided with any pro- 
tection of this kind. If the nasal cavities, the 
trachea or bronchia, the intestinal or urino- 
nital tracts, be examined in a healthy animal 
illed for the purpose, we may search in vain 
for any slimy covering, such as they are com- 
monly imagined to possess. But in a state of 
disease, each of these surfaces will secrete great 
quantities ; and it is nota little remarkable, that, 
even when healthy, if moistened and allowed to 
undergo slight putrefaction, they will become 
coated with a viscid fluid, having the physical 
characters of mucus. Yet the slimy fluid of the 
mouth cannot with propriety be considered 
abnormal. The true saliva is not viscid, as it 
escapes from the ducts of the glands into the 
cavity of the mouth: it probably becomes so 
by dissolving the substance derived from the 
scales of epithelium lining the mouth, as they 
advance to the surface and flatten. The fluid 
of ranula is not merely the accumulation of a 
natural secretion, but seems gradually to ac- 
quire its great viscidity by receiving the debris 
of the epithelium lining the excreting channels, 
and by the partial reabsorption of its aqueous 
portion. 
In the intestinal canal, however, although 
there is no viscid mucus naturally present, yet 
there is a large amount of“ inspissated mucus” 
being continually separated from the villi and 
follicles of Lieberkuhn. This mucus, as already 
mentioned, is nothing more than the debris of 
epithelial particles. 
But chemists have detected, in most of the 
secretions, a small proportion of a substance 
nearly allied to mucus, and probably a form of 
it. There is good reason to believe this to be 
the product of the membrane lining the ex- 
cretory passages, and to represent the old epi- 
thelium of that membrane. Where the secre- 
tion of the gland is fluid and in considerable 
quantity, it seems to be sufficient to convey 
away this debris from the surface which it tra- 
verses on its way out of the system, as in the 
salivary and allied glands, the liver, kidney, 
&c. But where, from the absence of this 
means of carrying off the debris of the epithe- 
lium, it might be supposed to be liable to 
accumulate and clog the surface, cilia are de- 
veloped ; of which the best example is fur- 
nished by the respiratory tract, the nasal ca- 
vities, and the tympana. That this is the 
great office of these wonderful organs upon 
these extensive surfaces appears to be proved 
by the fact that the currents they produce are 
uniformly towards an outlet. Henle has ob- 
served this in several parts, and I have-ascer- 
MUCOUS MEMBRANE. 
tained it by experiment in the case of thetra~ — 
cheal and bronchial membrane. iv 
In this tract no secretion is visible with the 
naked eye, but with the aid of the microscope — 
I have found, in perfectly recent animals, mi- 
pute globules of —— tenuity and of va-— 
rious sizes, which had the pearance ie 
mucus oozing from the smadieahdon'el the epithe- — 
lial particles. It is impossible but that “, 
cilia should move these globules along the 
face,and discharge them into the pharynx ; 
it hardly admits of doubt that mucus, morbidly 
existing on the bronchial membrane, is gradu; 
ally lifted up by these untiring agents to t 
region where it excites coughing, and is foreibly 
expelled by the rush of air. The patient is 
often conscious of its slow motion upw 
when it is in the form of a pellet and proc 
from an isolated spot. This is remarkably 
case too in hemoptysis, and also in that rare 
disease the bronchial polypus, where branched 
tubes of lymph are brought up in this m 
This view of the use of cilia in the muc 
system of the higher animals appears to me te 
merit much attention. I had intended to have 
considered it under a separate head, but it b 
been introduced here both in corroboration: 
the general position as to the nature of 
tion, and in illustration of the nature and ex 
of the special secretion from the ordinary & 
cous membranes. . 
On the whole I think it may be concluded 
1. That every part of the mucous sy 
where epithelium exists, secretes. “ 
2. That the secretion differs, in different 
gions, according to the vital properties of th 
epithelia; and that these vital agree: ; 
usually attended with appreciable varieties of 
structure. That corresponding varieties of che- 
mical constitution coexist with these is highly 
probable, though only as yet proved ina few 
cases. x 
3. That mucus is the least peculiar of the 
secretions, yet by no means universal from t 
mucous membranes, but confined to tracts” 
comparatively limited fe pre extent, chi 
the excretory channels of the glands. : 
In the preceding summary account of th 
structure, relations, and offices of the mucow 
system, I have not been able (without inter 
— to the course of the description) 
refer sufficiently to the labours of those ar 
mists to whom we owe almost all our kno 
ledge of the subject. This deficiency, of 
I am very sensible, I shall endeavour in soi 
degree to supply by a brief review of the 
searches which have led to the more mode 
and general views on the subject. SI 
over the imperfect descriptions of the anc 
we find that when the microscope first beca 
an instrument of anatomical research, the se 
character of the cuticle was recognised by M 
pighi and Leeuwenhoeck ; and that the form 
of these great anatomists had a wonderfully ¢ 
insight, considering the period at which he I: 
into the close relation that subsists between f 
glands, mucous membranes, and skin. TI 
labours of the anatomists of the next age we 
spent with great success upon matters of det 
~ S 
= any 
