As a result of the principles just enumerated, it may be said that there are three distinct and essential conditions for the successful disposal of sewage through the soil. These three conditions are, first, a rate of application suitable to the soil which it is proposed to use; second, an interrupted or intermittent delivery of the sewage so that the bacteria can obtain, between consecutive doses of sewage, the necessary amount of oxygen for their own preservation and well-being; and, third, a resting period in which is carried forward that intimate association between the partly decomposed organic matter and the oxygen or air present in the pores of the soil by which the final oxidation is obtained. The rate of application varies, as already indicated, with the size of particles found in the soil, and it should also vary with the purification desired. The larger the particles, the higher may be the rate of application, but less efficient will be the process. With grains of sand as fine as 1/200 of an inch, and with a rate of application not greater than five gallons per square yard of surface per day, filtration through such an area has been proved to be capable of removing from the foulest sewage all the objectionable material and converting the liquid into what is an equivalent of the purest spring water. If the rate appropriate to this particular soil is exceeded, the efficiency decreases, and the unmistakable and inevitable result is to stop all purification and convert the filter into a stagnant cesspool. If, to take the other extreme, the soil particles are increased until they are as large as hen’s eggs, then, if the rate of application is not greater than 200 gallons per square yard of surface per day, and if the method and rate of application are suitable to this large amount, the resulting effluent is sufficiently freed from its objectionable matter so that the liquid can be turned into any body of water without danger of odors or other nuisance. If this rate is exceeded, or if the method of application is not carefully considered, the resulting effluent is foul in the extreme and the process itself becomes a nuisance.