If we descend by degrees from great to small, from strong to weak, we
find that Nature has uniformly maintained a balance throughout her
works; attentive only to the preservation of each species, she creates
a profusion of individuals, and supports by numbers those she has
formed of a diminutive size, and left unprovided with arms, courage, or
resources; she has not only enabled these inferior species to resist
and maintain their ground by their own numbers, but has added a kind of
supplement to each, by multiplying the neighbouring species. The rat
(_fig. 74._), the mouse (_fig. 76._), the field mouse (_fig. 77._),
the water-rat (_fig. 75._), the short-tailed field mouse (_fig. 78._),
the dormouse, the shrew mouse, with several others, which I shall not
mention here, because they do not belong to our climate, form so many
distinct and separate species, but yet so little varied, that should
any one chance to fail, its absence would be hardly perceptible. It is
this great number of approximate species that first gave naturalists
the idea of genera, an idea which can only be employed when we view
objects in the gross, but which vanishes when we apply it to reality,
or when we consider Nature minutely.
Men began by appropriating different names to objects which appeared
to them distinctly different, and at the same time, they gave general
denominations to such as seemed to resemble each other. Among
unenlightened nations, and in the infancy of languages, there are
hardly any but general names, or vague or ill-formed expressions for
objects of the same order, though in themselves highly different. Thus
the oak, beech, linden, fir, yew, pine, had at first no name but that
of tree; afterwards the oak, beech, and linden, were called oak, when
they came to be distinguished from the fir, pine, and yew, which in
like manner would be called fir. Particular names could proceed only
from a minute examination of each species, and of course those names
would be increased in proportion as the works of Nature were more
studied and better understood; the more they studied her, the more
generic and specific names would be introduced. To represent Nature,
therefore, by general denominations, or genera, is to refer us back
to the dark and infant state of human knowledge. Ignorance produced
genera, but science will ever continue to create proper names; and we
shall not be afraid of increasing the number whenever we have occasion
to delineate different species.
Under the generic name of rat several species of little animals have
been comprised and confounded; but we appropriate this name solely
to the common rat, which is of a blackish colour, and lives in our
houses; they generally inhabit barns and granaries, from whence, when
food is scarce they invade our dwellings. The rat is carnivorous, or
if the expression may be allowed, an omnivorous animal; he prefers
hard substances to soft ones, he gnaws wool, linen, and furniture
of all sorts; eats through wood, makes holes and hiding places in
walls, ceilings, and behind wainscots, from whence he issues in search
of food, and frequently returns with as much as he can drag along,
forming, especially when he has young to provide for, a magazine of
the whole. The females bring forth several times in the year, though
mostly in the summer, and have five or six at a time. They love warmth,
and in winter they generally shelter themselves near chimneys, or
among hay and straw. In defiance of cats, poison, and traps, these
animals multiply so much as frequently to do considerable damage.
In old country-houses, where great quantities of grain are kept, and
where neighbouring barns and hay-stacks favour their retreat and their
increase, they often become so numerous that the inhabitants are under
the necessity of quitting their dwellings, unless they happen to devour
each other, and this is no uncommon thing when they are straightened
for provisions; for in case of a famine being occasioned by their
numbers the strong kill the weak, open their heads, first eat the
brains, and then the rest of the body: the next day hostilities are
renewed in the same manner, nor do they suspend their havock until the
majority are destroyed; and this is the reason why, in a place that
has been for some time infested with rats, they seem to disappear of a
sudden, and return not for a long time. It is the same with field-mice,
whose prodigious increase is checked solely by their cruelties to each
other when provisions become scarce. Aristotle attributes their sudden
destruction to the effect of rains, but rats are not exposed to the
weather, and field-mice know well how to secure themselves from its
effects, for their subterraneous habitations are not even moist.
Rats are as lascivious as voracious; they have a kind of yelp in their
amours, and when they fight they cry. They prepare a bed for their
young, and almost immediately provide them with food; and when they
first quit their hole the mother watches, defends, and will even fight
the cats to save them. A large rat is more mischievous, and almost as
strong as a young cat; its fore-teeth are long and strong; and as the
cat does not bite hard, but is obliged to depend upon her claws, she
must not only be vigorous but well experienced in warfare. The weasel,
though smaller, is yet a more dangerous enemy, because he can follow
the rat into its hiding places: the combat between these two is often
sharp and long, from their strength being nearly equal, but their
manner of fighting is different. The rat can only wound by snatches,
and with his fore-teeth, which are more calculated for gnawing than
biting, and have but little strength; whereas the weasel bites fiercely
with his whole jaw, and instead of letting go sucks the blood thro' the
wound, and therefore the rat always falls a victim to this formidable
enemy.
There are many varieties in this species, as in all those which have
numerous individuals. Besides the common rat which is nearly black,
there are some brown, grey, reddish, and quite white. The white rat,
like all animals perfectly white has red eyes. The whole species, with
all its varieties, appear to be natives of temperate climates, and have
been diffused in much greater abundance over warm countries than cold
ones. Originally they had none in America, but were transported with
the first European settlers, and where they increased so fast as to
become the pest of the colonies, and where indeed they had no enemies
but the large serpents which swallowed them up alive. The European
ships have also carried them into the East Indies, all the islands of
the Indian Archipelago, and into Africa, where they are now found in
great numbers. In the north they have never multiplied beyond Sweden,
and those which are called Norway and Lapland rats, are animals of a
different species.