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 yet more elaborate purification. At every stage in this process, a phial of water is taken out and examined in a dark chamber by means of a beam of light emanating from a powerful electric lamp and concentrated by a huge crystal lens. If this beam detect any perceptible dust or matter capable of scattering the light, the water is pronounced impure and passed through further processes. Only when the contents of the bottle remain absolutely dark, in the midst of an atmosphere whose floating dust renders the beam visible on either side, so that the phial, while perfectly transparent to the light, nevertheless interrupts the beam with a block of absolute darkness, is it considered fit for human consumption. It is then distributed through pipes of concrete, into which no air can possibly enter, to cisterns equally, air-tight in every house. The water in these is periodically examined by officers from the waterworks, who ascertain that it has contracted no impurity either in the course of its passage through hundreds of miles of piping or in the cisterns themselves. The Martialists consider that to this careful purification of their water they owe in great measure their exemption from the epidemic diseases which were formerly not infrequent. They maintain that all such diseases are caused by organic self-multiplying germs, and laugh to scorn the doctrine of spontaneous generation, either of disease, or of even such low organic life as can propagate it. I suggested that the atmosphere itself must, if their theory were true, convey the microscopic seeds of disease even more freely and universally than the water.

"Doubtless," replied our guide, "it would scatter them more widely; but it does not enable them to penetrate and germinate in the body half so easily as