Figures 52 and 53 represent sections of large Paris sewers. They carry both the house drainage of all kinds and the street washings and rain or storm water. They come under the "combined" system of sewerage as distinguished from the "separate" system in which rain water is separated from the house wastes.

The egg-shaped sewer (Fig. 50, initial cut) is the usual form now employed. Where a flat invert is used, as in Fig. 50, greater convenience is obtained for cleaning the flat portion, giving better foothold for the men. But for the conveyance of small quantities of sewage the regular egg form is better.

The section, Fig. 53, shows a form of sewer in which the gas pipes are submerged in a channel on one side filled with water to prevent leakage of gas.

The advantage of the separate system is that the flow is uniform and the dilution of the sewage is at its minimum, in which condition the valuable manurial part can be separated and the water purified and emptied into rivers or the ocean at a minimum of expense. In places where the grades are such that the rain water can be carried off in surface gutters to the ocean or river courses, the expense of the separate system is obviously much less than would be the combined. But where a double system of sewers would be required, as, for instance, in Paris, the cost would be greatly increased. The section in Fig. 55 shows a method by which the separate system might be used in a single sewer pipe, the drain water being shown in its maximum flow in the larger conduit and the house. sewage in the smaller. By carrying the rain water pipes from the street gutters overEgg-Shaped the house drainage conduit the position of their outlets might be so adjusted with reference to the latter that the first washings of the street would fall into it, and the storm water, as the storm increased in volume, would afterwards leap over it and fall into the larger conduit.

Fig. 52. Section of Paris sewers.

Fig. 52. Section of Paris sewers.

Fig:. 53. Section of Paris sewers.

Fig:. 53. Section of Paris sewers.

Fig. 50. Section of Sewer.

Fig. 50. Section of Sewer.

Whatever system be adopted, the sewer should be ventilated sufficiently often to render the air in the sewer perfectly pure, and such ample light should be provided as to give the double advantage of convenience of inspection and the freedom from the undesirable anaerobic germs to which strong light is inimical.

Frankland shows in a plate we have reproduced in Fig. 56 in a very interesting manner, the effect of sunlight on disease germs. He placed the letters spelling the name of the particular disease germ upon which he experimented, cut out of opaque paper, upon a plate of gelatine inoculated with the germ, and exposed the plate to diffused sunlight. The germs protected by the paper letters multiplied rapidly, while all those in the unprotected parts of the plate were destroyed, so that when the paper had been removed the disease germs had written their own autograph, as shown in the picture.

Fig. 55. Writer's method of combining both conduits of the separate system of sewerage in a single sewer.

Fig. 55. Writer's method of combining both conduits of the separate system of sewerage in a single sewer.

Ample lighting as well as ample ventilation is a sanitary measure everywhere.

The inner surfaces of all sewers should be lined with glazed materials, and in large sewers with white glazed or enameled tiles to increase the light reflection and insure greater cleanliness.

Now that draught animals in our streets are gradually being supplanted by machine motors, the streets will soon be paved with smooth materials and be kept perfectly clean.

Fig. 56. Autograph of cholera germs.

Fig. 56. Autograph of cholera germs.

This will tend to greatly simplify sewerage and effect a much more general adoption of the separate system enabling us to come much nearer the ideal of waste water purification and recovery of its useful manurial part, at a minimum of outlay.

Figs- 57 and 58 show old Paris sewers, the illustrations being taken from Victor Hugo's "Les Miserables." These sewers carried the storm waters and house drainage with the exception of part of the W. C. refuse which was at that time almost exclusively collected in cesspools. Today the cesspools are gradually being removed and everything will soon be conducted directly into the sewers. The waste from the street urinals and the liquid overflow from the house cesspools was, however, taken into the sewers long before the crusade against cesspools was undertaken. Nevertheless the sewage today contains probably far more water in proportion to the bacteria within than it did at the time of Jean Valjean, because the supply of water to the closets fully offsets any additional impurity they furnished. Moreover, sink water and urine form the most dangerous parts of the house water. But the unscientific manner in which these old sewers were constructed and operated made them little better than elongated cesspools, as compared with the magnificent and cleanly conduits they appear today.

In 1882 Paris still had 80,000 cesspools and 30,000 shallow drinking water wells, most of which were contaminated and entirely unfit for use.

These pictures show the appearance of the old Paris sewers in 1805, when Bruneseau visited them with a view to their improvement. Fig. 57 presents the engineer making what Victor Hugo calls "the formidable campaign" - the "nocturnal battle against asphyxia and plague." Eight out of the twenty workmen gave up the battle in the middle of it. The ladders for measuring would sink three feet deep in mud, and the lanterns would scarcely burn in the mephitic atmosphere, the men fainting from time to time. There were horrible pits in the ground in which one man suddenly disappeared. The walls were hanging with fungi. Among other things they found the skeleton of an ourang-outang, which had disappeared from the Jardin des Plants in 1800 and drowned itself in the sewer. They found, also, on the other hand, valuable objects, coins, gold and silver, jewelry and precious stones.