The couple multiplied rapidly, until whole families of equal whiteness ascended and descended the staircases of the cage. At last we found ourselves at the head of thirty rats, all so much at home with us that when the weather was cold they burrowed in our pockets without the least ceremony, and lay there, keeping themselves warm. Sometimes leaving open the door of the Ratopolis, we would go up to the second floor of the house, and give a whistle well known to our pupils. Then the tiny crew, who with great difficulty could climb from one step of the stairs to the other, would swarm upward, clutching the rail, pulling themselves along by the balusters, following each other in a file with the regularity of acrobats, up the steep road, down which occasionally one slipped, and run to find us, uttering little cries and manifesting the liveliest joy. We must now confess to an act of brutality. We had so often heard it said that a rat’s tail resembled a pink worm and detracted from the beauty of the animal, that at last we selected one from our menagerie, and cut off the much-abused appendage. The little rat bore the operation well, grew up bravely, and became a master rat, with a fine pair of moustaches; but in spite of being lightened of the weight of his caudal extremity, he was always less agile than his companions, was wary in gymnastic exercises, and frequently experienced a tumble. When the troop ran up the staircase, he invariably came last; and he always had the air of an acrobat who is testing his tight-rope and is not quite sure of his balance. This experiment convinced us of the usefulness of a tail to rats. It holds them in equilibrium as they run along cornices and narrow projections. When they swiftly turn to right or left the tail turns too, serving as a counterpoise; and this is the cause of the perpetual wiggle which characterizes it. Nature seldom makes a superfluous thing, and for this reason we should be very cautious in trying to improve her handiwork.