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TIARIDIUM. 
inches in length from the crown of the root; its 
flower-stems arise from among the leaves, and 
attain a height of from 4 to 6 inches; and its 
flowers grow in loose terminal spikes, and are 
small, of a herbaceous white colour, and bloom 
in April and May. Two other species of similar 
character, but with taller flower-stems, have 
been introduced from North America and Ne- 
paul; and all are propagated by radical division. 
TIARIDIUM. A small genus of ornamental, 
tender, blue-flowered, annual plants, of the bor- 
age ‘Evailly, Two species, the velvety and the 
Thai any both about a foot high, have been intro- 
duced to Britain from the West Indies. 
TICK. A parasitical insect, similar to a louse, 
and infesting sheep and dogs. It is many times 
larger than a louse, and of a different colour, but 
not of so frequent occurrence. It varies in size 
from a pin’s head to a small bean, but is com- 
monly about as big as a pea; and when not 
gorged with blood, it is flat,—but, when bloated, 
is round and of a brown or black colour. It has 
six legs, and runs with much speed ; and attaches 
itself to the skin by means of sharp claws at the 
extremity of the legs, and pierces the skin by 
means of sharp instruments in its head; and 
when once it fastens on a spot, it seems to re- 
main quite fixed for several weeks or even 
months; and it becomes surrounded with num- 
erous young ones, who appear at first like red 
points, but afterwards acquire a brown colour as 
they grow. It propagates rapidly; and is often 
found in great numbers on a single sheep; and 
commonly prefers the animal’s neck and should- 
ers to other parts. It is thought by some per- 
sons to breed upon the ground, and to spend only 
the later stages of its existence upon sheep; and 
certainly it frequents some farms and districts 
far more than others, and is seldom found on 
some badly managed farms where it might natu- 
rally be expected, and cannot without great diffi- 
culty be banished from some well-managed farms 
and very healthy flocks where it might be sup- 
posed not at all to occur. It is, of course, a sad 
pest to the animals whom it affects, destroying 
their peace, diminishing their fleece, and dis- 
turbing the general economy of their health 
and growth; and it ought, in every case, to be 
promptly and exterminatingly attacked. One 
effectual remedy is rubbing with mercurial oint- 
ment, but is liable to produce salivation or dan- 
gerous exposure in unsuitable seasons or weather; 
another effectual remedy, at times when the mer- 
curial ointment cannot be prudently applied, is 
washing with tobacco-water, but lies under the 
disadvantage of giving a depreciating tinge to 
the wool; another efficient remedy, at all times, 
is dipping in a. solution of arsenic, but involves 
the risk of terrific casualties to both man and 
beast from the use and presence of so dreadfully 
poisonous an agent; another always efficient 
remedy is washing with a lotion of one ounce of 
corrosive sublimate, one-fourth of a pint of spirit 
of wine, and three quarts of water, but is liable, 
in a large degree, to the same objection as the 
preceding; another, almost equally efficient, and 
somewhat less objectionable, is washing with a 
lotion of two ounces of tobacco, 23 ounces of soft 
soap, 11 lbs. of white calx of mercury, and 8 gal- 
lons of water; and another, considerably less 
efficient, but correspondingly, less unobjection- 
able, is the application of linseed oil or of tur- 
pentine. Careful hand-picking is practised by 
some shepherds; and of course is efficient as far 
as it goes, but, in all bad cases, is an endless and 
quixotic task. See the articles Sunup, Sanvine 
or SHExp, and Friy-1n-SHEnp. 
TICKSHED, — botanically Corispermum. A 
genus of exotic herbaceous plants, of the goose- 
foot family. About a dozen species, all hardy 
apetalous annuals, blooming about the end of 
summer, and varying in height from 6 to 20 
inches, have been introduced to the botanical 
collections of Britain, principally from Eastern 
Kurope and Northern Asia; and some other 
species are known. Both the popular and the 
botanical names refer to the bug-like form and 
appearance of the seed. 
TIDES. The ebb and flow of the sea are evi- 
dently connected with the moon’s motions. The 
level of the ocean is slightly disturbed by the 
attraction which is alternately exerted and with- 
drawn. The waters, for a large space under the 
moon, being more attracted than the great body 
of the earth, are thus rendered lighter than 
those parts of the ocean which are at the same 
distance as the earth’s centre; and, being lighter, 
they are forced upwards a little by the surround- 
ing mass, which is heavier; just as water and oil 
will stand at different heights in the two branches 
of a siphon tube; or just as ice, which is lighter 
than water, is made to rise a little higher, on 
that account, when placed in water. If the 
earth rested immoveably upon a fixed support, 
there would be a tide, or rising of the waters, 
only on the side towards the moon. But the 
great body of the earth is just as free to move as 
a single particle of the ocean, and, if suffered to 
yield to the moon’s attraction, would be carried 
just as fast. Hence, for the same reason that a 
particle of water, on the side of the earth towards 
the moon, is drawn away from the centre, or has 
its downward tendency diminished, so the solid 
earth itself is drawn away from the mass of wa- 
ters, on the side of the earth farthest from the 
moon. It is the difference of attraction in both 
cases, between the surface and the centre, which 
causes the lightness of the waters, and the con- 
sequent elevation. It will be seen, therefore, 
that, taking the whole earth into view, there are 
always two high tides diametrically opposite to 
each other, and two low tides also, mid-way be- 
tween the high ones. The high ties are two 
great waves, or swells, of small height, but ex- 
tending each way through half a right angle. 
These waves follow the moon in its namin 
(a a a ae 
