One of the chief sanitary safeguards in Nature is dilution. A small amount of pollution may be quickly diluted by a volume of water until it is practically harmless. In its concentrated state, however, there might be enough poison, the strength of which would be greater than the internal resistance of the individual. This would produce toxic conditions, or it might even be great enough to produce subluxations. =Sedimentation= is another of Nature’s methods that is of great value. This process has been aped by man in the coagulation produced by the use of chemicals. This action is largely mechanical. During the process of sedimentation it is only the suspended matter that settles; but it is maintained that the bacteria and microörganisms become entangled and are carried to the bottom and in this way the water is freed from more than simply the mechanical impurities. If allowed to remain in storage a sufficient time, the harmful bacteria will die a natural death. There are processes, however, that take place during the time of storage which are objectionable, but these relate more to the taste or smell of the water than to the production of harmful ingredients. During sedimentation there is a natural settling of the suspended particles. Not only is the desired result obtained in freezing the water of solids, but as the suspended matter sinks to the bottom many of the bacteria will also be carried down. Sedimentation, however, is not a method that can be used promiscuously. It is usually employed in connection with some other method; with a slow sand filter, for example, or when mechanical filtration is used. Sunlight is Nature’s greatest germicide. Direct sunlight destroys germ life and renders much aid in maintaining sanitary environmental conditions. It has a purifying effect upon water in this way. When the water is in motion or during times of turbidity great good is accomplished from a sanitary standpoint by the direct rays of the sun. Artificial Methods of Water Purification The only way to obtain chemically pure water is by distillation. However, since this method is very slow and expensive, it is not at all practicable for the purification of even a private water supply, and since a chemically pure water is not required for drinking or other domestic purposes it would be entirely unnecessary to provide it. Again, distilled water is not desirable for drinking purposes since its taste is insipid until it is aerated. When only a small amount of water is required it may be freed of organic poisonous substances by boiling. This will not, however, render water that contains lead and other stable chemical substances injurious to health safe for domestic use. [Illustration: Sand Filter.] The dissolved gases are given off by boiling and this leaves the water with a flat taste which may be improved by aerating; this may be done by stirring or by placing the water in a jar and shaking it.