But in this same thoroughfare one may often witness a spectacle less resplendent, with groups aught but gay. Midway along the street runs a deep drain or sewer, not as in European cities permanently covered up, but loosely flagged over, the flags removable at will. This, the _zanca_, is more of a stagnant sink than a drainage sewer; since from the city to the outside country there is scarce an inch of fall to carry off the sewage. As a consequence it accumulates in the zancas till they are brimming full, and with a stuff indescribable. Every garbage goes there--all the refuse of household product is shot into them. At periodical intervals they are cleared out, else the city would soon be a-flood in its own filth. It is often very near it, the blue black liquid seen oozing up between the flagstones that bridge over the zancas, filling the air with a stench intolerable. Every recurring revolution make the municipal authorities of Mexico careless about their charge and neglectful of their duties. But when the scouring-out process is going on, the sights are still more offensive, and the smells too. Then the flags are lifted and laid on one side--exposing all the impurity--while the stuff is tossed to the other, there to lie festering for days, or until dry enough to be more easily removed. For all it does not stop the circulation of the carriages. The grand dames seated in them pass on, now and then showing a slight contortion in their pretty noses. But they would not miss their airing in the Paseo were it twenty times worse--that they wouldn't. To them, as to many of their English sisterhood in Hyde Park, the afternoon drive is everything--to some, as report says, even more than meat or drink; since they deny themselves these for the keeping of the carriage. It may be imagined that the scouring-out of the zancas is a job for which labourers are not readily obtained. Even the _pelado_ turns up his nose at it, and the poorest proletarian will only undertake the task when starvation is staring him in the face. For it is not only dirty, but deemed degrading. It is, therefore, one of the travaux-forces which, as a matter of necessity, falls to the lot of the "gaol-bird." Convicts are the scavengers; criminals sentenced to long periods of imprisonment, of whom there are often enough in the _carceles_ of Mexico to clean out all the sewers in the country. Even by these it is a task looked upon with repugnance, and usually assigned to them as a punishment for prison derelictions. Not that they so much regard the dirt or the smells; it is the toil which offends them--the labour being hard, and often requiring to be done under a hot, broiling sun.