For the _wagonnets de service_ in the larger sewers, an ingenious arrangement is used,--on the little four-wheeled truck which runs on rails along the edge of the central canal are laid two more sections of railroad at right angles, and on these are mounted two more four-wheeled trucks carrying each a rectangular little tank or receptacle, with a rounded bottom. The outside rail, at each end, is blocked, so as to keep these tanks in position while in transit,--when arrived at their destination, the blocks are removed and the two run off on other rails to be emptied. The Parisian sewers carry not only the drainage of the streets and houses, but also all those various underground means of communication which in other, and less well-ordered, municipalities have each their own burrowing to do,--at the cost of infinite expense and confusion. The water-pipes, the telegraphic cables, the telephone wires, the pneumatic tubes for the postal service, and the piping for the conveyance of motive power, are all sheltered in these underground thoroughfares. So complete and well organized, indeed, are these égouts, that that constant habitant of sewers, the rat, is being driven out of them,--neither the black rat nor his enemy, the great Norway animal, can find lodging and refuge in these cement-lined walls, as hard as steel. The task of the hunter of rodents is greatly facilitated by all these improved methods. It is difficult nowadays to conceive the condition of the streets of a mediæval city, and Paris was no exception. Not only were they very crooked--each householder building where he chose, with very little consideration for the general alignment, badly paved or not at all, unsewered and dark, but they were the receptacles for absolutely all the refuse of the dwellings. The butcher, the baker, and the candlestick-maker threw everything out of the windows, and nobody carried it away. The first vaulted sewer was constructed in the reign of Charles VI, in the Rue Montmartre, by Hugues Aubriot, _prévôt_ of the merchants; but the state of the public thoroughfares remained much as it had been in the preceding century. The houses were built on the level of the streets, and inundated at every violent shower, the choked-up gutters refusing to carry off the sudden flood. Even the kings of France struggled in vain against the universal infection,--"incommoded in their Hôtels Saint-Pol and des Tourelles, they were constantly protesting to the municipality of Paris; Louis XII, François I, and Henri II vainly attempted to secure the removal of the égout Sainte-Catherine; this unwholesome neighborhood even caused François I to change his property of Chanteloup for the locality of the Tuileries." In 1473, the Parlement ordered the Lieutenant Criminel to clear away the filth which obstructed the entrance to Saint-Nicolas-du-Chardonnet and along the course formerly traversed by the Bièvre, and three years later a more general effort at reformation was made.