“The common or black rat is more than twice the size of a mouse. Its coat is nearly black above, and ashy gray underneath. It lives in granaries, thatched roofs, and abandoned ruins. If it fails to find a lodging to its taste, it burrows a hole for itself. It is not a native with us, but is thought to have come from Asia in the wake of the armies returning from the Crusades. To-day the common rat is seldom mentioned in our country; another foreign rodent has come in, the Norway or brown rat, which, being larger than the common rat, has waged war against it and almost wiped out the species. We have not gained by the exchange; quite the contrary, the Norway rat being a much more troublesome creature. The true rat, the black rat, is rare now, especially where the other abounds; and that is why I doubt that any one of you is familiar with it. What you call a rat is more than likely to be one of these Norwegian invaders. Don’t forget the color—black—and you will have no difficulty in recognizing the true rat. “The mouse is much more familiar to you. It has been known from the earliest times all over the world. Need I describe this little rodent, so well known for its liveliness, its wily nature, and its extreme timidity, which makes it scuttle away to its hole at the slightest alarm?” “We all know the mouse very well,” Jules assured him. “The Norway or brown rat, also known as the sewer-rat, is the largest and most troublesome of all European rats. It attains a length of nearly a foot, without counting the tail, which is scaly like the mouse’s and a little shorter than the body. The largest and strongest Norway rat can cope with a cat. Its presence in Europe dates only from the middle of the eighteenth century, and it seems to have been brought from India in the hold of ships, which it commonly infests. It has now spread all over the world. Its coat is reddish brown above and ashy gray underneath. “Norway rats frequent storehouses, cellars, sewers, slaughter-houses, and dumping grounds. Everything is food to these filthy and audacious creatures, and they even dare to attack a sleeping man. In large towns they multiply so fast as to cause serious alarm. The vicinity of the slaughter-house of Montfaucon in Paris is so undermined with their innumerable burrows that the buildings there are in danger of collapsing. To preserve them from this disaster it is necessary to protect their foundation against the attacks of the rodents by means of a deep enclosing belt of broken glass bottles.” “What attracts them in such numbers to these places?” asked Jules.