GUA 
face as to receive the full influence of the 
air and sun shine ; but should unfavourable 
weather again take place, they again sink 
the precious deposit, and thus preserve it 
from danger. The young at their first ex- 
clusion are about the size of ants, for which, 
on a cursory view, they might be mistaken : 
but on a close inspection are easily known 
by their broad feet, &c. In about the 
space of a month they are grown to the 
length of more than a quarter of an inch ; 
in two months, upwards of three quarters ; 
and in three months, to the length of more 
than an inch. Of this length they are 
usually seen during the close of autumn, 
after which they retire deep beneath the 
surface ; not appearing again till the ensuing 
spring. During their growth they cast 
their skin three or four times. The mole- 
crickqt lives entirely on vegetables, devour- 
ing the young roots of grasses, corn, and 
various esculent plants, and commits great 
devastation in gardens. 
5. G. tettigonia, or grasshopper, well 
known in our meadows, belongs to this 
genus. 
GUAIACUM, in botany, a genus of the 
Decandria Monogynia class and order. 
Natural order of Gruinales. Rutaceae, Jus- 
sieu. Essential character : calyx five-cleft, 
unequal ; petals five, inserted into the re- 
ceptacle; capsule angular, five-celled. There 
are four species. From the G. officinale, is 
obtained a resin which exudes spontaneous- 
ly, and is also driven out artificially by 
means of heat. This substance has been 
long known and celebrated as a medicine 
in various cases ; and in the Transactions of 
the Royal Society for the year 1806, we 
have a very complete analysis of it : by dis- 
filiation 100 parts yielded 
Acidulous water 
Thick brown oil 
Thin empyreumatic oil 
Charcoal 
Gases consisting of carbo- ' 
nic acid and carbureted 
> 10.5 
liydreaen ) 
100.0 
Hence it is inferred that guaiacum agrees 
in many respects with the resins, 
but it dif- 
fers from them, 1. in the quantity of char- 
coal it leaves when distilled in close vessels ; 
2. in the action that nitric acid has upon it ; 
and, 3. in the changes of colour that it un- 
dergoes when its solutions are treated with 
nitric and oxymuriated acids. Its proper- 
G UA 
ties may be thus enumerated : it is a solid 
substance resembling a resin ; its colour 
varies, but is generally greenish ; it is 
readily dissolved in alcohol ; alkaline solu- 
tions dissolve it with ease : most of the 
acids act upon it with considerable energy ; 
if digested in water, a portion is dissolved, 
the water acquiring a greenish-brown co- 
lour : the liquid being evaporated, leaves 
a brown substance which possesses the pro- 
perties of an extract, being soluble in hot 
water and alcohol, but scarcely at all in 
sulphuric ether, and forming precipitates 
with the muriates of alumina, tin, and 
silver. 
GUANA. See Lacerta. 
GUANO, a substance found oil many of 
the small islands in the South Sea, which 
are the resort of numerous flocks of birds, 
particularly of the Ardea and Phaenicopte- 
rus genus. It is dug from beds fifty or 
sixty feet thick, and used as a valuable ma- 
nure in Peru, chiefly for Indian corn. It 
is of a dirty yellow colour, nearly insipid to 
the taste, but has a powerful smell, partak- 
ing of castor and valerian. According to 
the analysis of Fourcroy and Vauquelin, 
about one-fourth of it is uric acid, partly 
saturated with ammonia and lime. It con- 
tains likewise oxalic acid, partly saturated 
with ammonia and potash ; phosphoric acid 
combined with the same bases and with 
lime ; small quantities of sulphate and mu- 
riate of potash and ammonia ; a small por- 
tion of fat matter ; and sand, partly quart- 
zose, partly ferruginous. 
GUARD, in a general sense, signifies the 
defence or preservation of any thing ; the 
act of observing what passes, in order to 
prevent surprise ; or the care, precaution, 
and attention we make use of, to prevent 
any thing happening contrary to our inten- 
tion or inclinations. 
Guard, in the military art, is a duty 
performed by a body of men, to secure 
an army or place from being surprised by 
an enemy. 
In a garrison the guards are relieved every 
day, and it comes to every soldier’s turn 
once in three days, so that they have two 
nights in bed, and one upon guard. To be 
upon guard, to mount the guard, to dis- 
mount the guard, to relieve the guard, to 
change the guard, the officer of the guard, 
or the seijeant of the guard, are words often 
used, and well understood. 
Guard, advanced, is a party of either 
horse or foot, that marches before a more 
