In spite of the fact that the lack of air in the water will prevent bacterial action, there are, nevertheless, many cases where the discharge of sewage into a stream may be permitted as being the best solution of the disposal problem, provided always that the stream is not used and is not likely to be used for drinking water. Such cases occur where the stream is relatively large and where the level of the stream is fairly regular, so that there is no likelihood of the deposit of organic matter on the banks during the falling of the stream level. Examples of this sort might be cited in the vicinity of the Mohawk or Hudson River, or in the vicinity of any of the larger rivers of any populous state, since although the water of the Mohawk is used by the city of Albany for drinking purposes, yet the amount of organic matter which inevitably finds its way into such rivers precludes its use for drinking without filtration. Into the Hudson below Albany there can hardly be any question of the propriety of discharging sewage from a single house. Again, houses in the vicinity of large bodies of still water may without question be allowed to discharge into those lakes. For example, houses in the vicinity of Lake Ontario or Lake Michigan, or even of much smaller lakes, should not contribute any offensive pollution to the waters of the lake. In New York State, some of the smaller lakes are used as water-supplies for cities, as, for example, Owasco Lake for the city of Auburn and Skaneateles Lake for the city of Syracuse, and, acting under the statutes, special laws have been passed by the State Department of Health, forbidding any discharge of any kind of household wastes into these lakes. The same is done in other states. Here, again, it is a question of the drinking supply which is being considered, and not a question of the possibility of any nuisance being committed. _Treatment of sewage on land._ If no stream suitable for the reception of sewage is available, then the sewage must in some way be treated on land before it passes into the nearest watercourse. For the second fundamental principle about the treatment of sewage is that of all places the action of putrefactive bacteria is most energetic in the surface soil and that it is there that the organic matter of sewage can be most rapidly accomplished. Experiments already referred to have shown not only this, but also that their activity is most noticeable in the surface layers of the soil and that their action continues for scarcely two feet downward, and it is customary to assume that the largest amount of work done is accomplished in the top twelve inches. Further than this, it has been established that in order to persuade the bacteria involved to do their work as promptly as possible, the application of sewage to any particular locality should be made intermittent; that is, that a resting period should be given to the bacteria between successive applications of sewage.