liardentng in the sun into brittle and almost 
transparent lumps. 
MUCUS, amncilaginous liquor separated 
by the mucous glands, and the nostrils. 
Mucus. See Physiology. The che- 
mical properties of this substance are ; that 
it has the appearance of gum arabic, only 
more opaque ; it does not dissolve in alco- 
hol or ether , it does not coagulate when 
heated ; it is not precipitated by the oxy- 
muriate of mercury, nor by the infusion of 
galls ; the acetate of lead occasions a cor 
pious white precipitate when dropped into 
solutions containing mucus ; so does the 
nitrate of silver. It is generally combined 
with gelatine and albumen, and always 
with some of the sal ts, and on the whole it 
is one of the least abundant of the animal 
fluids. In its natural state it is generally 
colourless, but from peculiar causes it will 
frequently assume a thick consistence and 
whitish colour like pus. From some expe- 
riments made by tlie late Dr. Charles Dar- 
win, certain important conclusions have 
been drawn, for which the reader is referred 
to Medicine. 
MUFFLE, in metallurgy, an arched 
cover, resisting the strongest fire, and made 
to be placed over coppels and tests in the 
operations of assaying, to preserve them 
from the falling of coals and ashes into 
them ; though, at the same time, of such a 
form, as is no hindrance to the action of the 
air and fire on the metal, nor to the inspec- 
tion of the assayer. The muffles may be 
made of any form, providing they have these 
conditions 5 but those used with coppels 
are commonly made semi-cylindrical ; or 
when greater vessels are employed, in form 
of a hollow hemisphere. The muffle must 
have holes, that the assayer may look in ; 
and tliefore part of it must be always quite 
open, that the air may act better in con- 
junction with the fire, and be incessantly 
renewed ; the apertures in the muffle serve 
also for the regimen of the fire, for the cold 
air rushing into the large opening before, 
cools the bodies in the vessel ; but if some 
coals are put in it, and its aperture before 
be then shut, with a door fitted to it, the 
fire will be increased to the highest de- 
gree, much more quickly than it can be by 
the breathing holes of the furnace. See 
Assaying. 
MUGIL, the mnllet, in natural history, a 
genus of fishes of the order Abdominales. 
Generic character : lips membranaceous, 
the lower one carinated inwards ; no teeth ; 
above the corners of the mouth an inflected 
callous substance ; gill-membrane with se- 
ven curved rays ; body fleshy and whitish ; 
large scales ; two dorsal fins. Gmelin no-^ 
ticcs only five species. Shaw mentions 
nine. M. cephalns, or the common mullet 
is generally about fourteen inches in length, 
and is found not only in the Northern and 
Mediterranean Seas, but in the Indian and 
Western Oceans. These fishes collect in 
vast multitudes almost close to the shores, 
in quest of those aquatic insects which con- 
stitute their food, thrusting their heads into 
the soft muddy bottoms with incessant 
activitj . On the approach of summer they 
assemble in immense numbers to ascend ri- 
vers, which they do to a considerable dis- 
tance from the sea, in order to deposit their 
ova, and while they are thus assembled, the 
fishermen avail themselves of the transient 
opportunity, and, spreading their nets take 
them in extraordinary ahiradance. They 
are regarded by many as excellent, hut are 
not often seen at the tables of the opu- 
lent. 
MUHLENBERGIA, in botany, a genus 
of the Triandria Digynia class and order. 
Natural order of Gramina, Gramineas, or 
Grasses. Essential character : calyx one- 
valved, minute, lateral ; corolla tw'o-valved. 
There is but one species, viz. M. diffusa, 
which is a perennial grass, and a native of 
North America. 
MULBERRY. See Morus. 
MULE, in zoology, a mongrel kind of 
quadruped, usually generated between an 
ass and « mare, and sometimes between a 
horse and a she-ass. The mule is a sort of a 
monster, of a middle nature between its pa- 
rents, and tlierefore incapable of propagating 
its species; so careful is nature to avoid 
filling the world with monsters. Mules are 
chiefly used in countries where there are 
rocky and stony roads, as about the Alps 
Pyrenees, &c. Great numbers of them are 
kept in these places ; they are usually 
black, strong, well limbed, and large, being 
mostly bred out of the fine Spanish mares ; 
the mules are sometimes fifteen or sixteen 
hands high. No creatures are so proper 
for carrying large burdens, and none so 
sure footed. They are much stronger for 
draught than horses, and are often as thick- 
set as our dray-horses ; and they will travel 
several months together, with six or eight 
hundred weight upon their backs ; they 
are much hardier and stronger than horses 
and will live and work twice the age of a 
horse. Those nudes which are light are 
fitter for riding than horses, as to the walk 
and trot ; but they are apt to gallop very 
ronghly. See Equus. 
