Another system of drainage which the inspectors used very freely and found very useful, was that of filling the ditch, after it had been excavated, with broken stone. This largely prevented the growing of grass, and also prevented any development of mosquitoes in the ditch itself. Another form much resorted to was that of lining the ditch with concrete. This entirely prevented the growth of grass and did away with the expense of up-keep. The only expense involved in caring for such a ditch was that of a man going over it now and then and removing such obstructions as may have gotten in. Mr. Le Prince and his inspectors became very expert in this style of concrete work, and finally, by the use of chicken wire as a framework for strengthening the concrete, were enabled to lay a ditch of this type very cheaply. Wherever the drainage was expected to be used for a year or more, we found it more efficient and economical to use concrete rather than the open ditch. Mr. Le Prince and his staff devised several processes whereby the cleaning of these ditches of grass was much cheapened. Several solutions of arsenic were found which, when applied to the grass, killed it. Such a process kept the grass down for a much longer time than that of simply cutting it out with a hoe. A burner was devised which atomized oil under air pressure, making a very hot flame which destroyed the grass roots. After once clearing a piece of ground the inspector had to keep it in such condition that it would not protect adult mosquitoes. He had, therefore, not only to keep it clear of brush, but also must not allow the grass to grow more than a foot in height. For grass-cutting, there was a great economy in using the horse-mower wherever we could. Numerous open ditches interfered with the use of a horse-mower. To meet this difficulty, the inspector used sub-soil tiled drainage wherever it was feasible. This is the ideal anti-mosquito drainage. It carries off the water, so that there is no formation of breeding-places on the surface. After it is once laid it requires no work or expense for up-keep, and a horse-mower can be used just as freely over its surface as if there were no ditch there. With the various methods just mentioned we drained pretty well about one hundred square miles of territory, constructing in all some five million feet of open ditch, some one and a half million feet of concrete ditch, some one million feet of rock-filled ditch, and about one million feet of sub-soil tile.