And so, the chemist was not alarmed when he discovered that the formation of gas in his crooked tube gave indication of bacteria in the drinking water.  He must ascertain what type of bacteria he had entrapped.  To this end, he analyzed the gas, and when he determined that the fermentation was due to the presence of colon bacilli in the water, he sent out his warning.  Not that the colon bacilli are a menace to health.  The body of every human being in the world is infested with millions of them.  But the presence of colon bacilli in drinking water is an indication of the presence of a really dangerous thing—­sewage.

Thus, when the city chemist turned from his test tube with the exclamation, “Colon!” he did not fear the thing that he saw, but the thing that he knew might accompany it.

There has been much discussion of late of the possibility that the great lakes cities may suffer a water famine.  The rapid increase of population along the borders of these great seas, it has been said, might render the water unfit for use.  This fear is based upon the assumption that we shall always continue the present very foolish practice of dumping our sewage into the source of our water supply.  The time may come when we shall know better how to protect the public health and at the same time husband the public resources.  But even at that, the city chemist says that he hardly expects to see the time when the present intake for water near the head of Belle Isle will not be both safe and adequate.

No doubt he makes this statement because he has confidence that the purification of water is both simple and safe.  There are two principal methods.  The first, and most expensive, is nature’s own—­the filter.  The application of this method is comparatively simple though it involves considerable expense.  The trick was learned from the hillside spring which, welling up through strata of sand and gravel, comes out pure and clear and sparkling.  To make spring water out of lake water, therefore, it is merely necessary to excavate a considerable area to the desired depth and lead into it the pipes connected with the wells from which water is to be pumped.  Then the pit is filled with successive layers of crushed stone graduated in fineness to the size of gravel and then covered with a deep layer of fine sand.  This area is then flooded with the water to be filtered, which slowly percolates and comes out clear and pure.  The best results in purification of contaminated water supplies have probably been attained in this way; that is, as measured by the improvement of health and the general reduction of the death rate from those diseases caused by the use of contaminated water.

But when the alarm was given this spring by the city chemist there was no time to excavate and build an extensive filtering plant.  The dreaded typhoid was already making its appearance and babies were dying.  Something had to be done at once.