Another means by which the water of cisterns is contaminated is by their being placed in improper positions. Quite frequently, a cistern in which drinking-water is stored, is situated in, or even under the floor of a w.c. Burton has known more than one case in which the drip tray under a closet actually discharged into a cistern. It is even possible for contamination of water to occur through the mere fact that a water-closet is supplied from a certain cistern. With a water-closet supplied by the modern regulator-valve apparatus, this is most unlikely; but it will be readily seen how it may occur with such an arrangement as that shown in Fig. 20, which is common. Here it will be seen that for each water-closet there is a plug in the cistern. This plug is so arranged that when it is raised by the wire which connects it with the water-closet branch, it suddenly fills what is called a service box, this being a subsidiary cistern fixed under the body of the main cistern, and in direct communication with the water-closet. After the water has run out of the service box, this is free to fill itself with foul gas from the water-closet by the service pipe, and the next time the plug is lifted this same foul gas passes into the water, which absorbs a part of it. There are many other points in the drainage arrangements of a house which may possibly become causes of danger, such as surface traps in areas, &c. In speaking of the drain of a house, it has been considered as a single length of pipe; but it must be remembered that in any drainage system, except the most simple, there are branch drains, often many of them, and that these are liable to the same evils as the main drains, and require the same attention. In fact, seeing that less water is likely to pour down them, they require more attention. Burton concludes his paper with a brief description of the methods in use for discovering defects in house sanitation. One thing that is absolutely necessary for such inspection, and without which it would be quite incomplete, is to open down to the drain. This should be done at the nearest point to that at which it leaves the premises. There is no absolute guide to tell where this point is, but after some experience it is generally possible to hit upon the spot with very little searching. In the house illustrated in Figs. 20, 21, it would be under the front area or cellar. The ground should be entirely removed from the drain for at least two lengths of pipe. It is also very desirable that a portion of the ground over the top of the drain should be removed. We may next take the point of trapping of the main drain and ventilation of the system. It will be seen that, in the case of the drawing of the imperfect arrangements, the drain is shown to be in direct communication with the sewer. The consequence is that any leakage which may exist in the house drain permits gas not only from the drain itself, but from the sewer also, to find its way into the house.