Before we can properly judge of the relative merits of different systems of sewerage and plumbing, or of different kinds of appliances used in them, or of the effect of sewage decomposition upon our health, we must study the nature of the substances with which we have to deal. The discoveries of the last few years have radically altered our methods of treatment of sewage, both within and without the building. We have through these discoveries, learned why it is that sewage must be quickly removed from our neighborhood instead of being allowed to remain in cesspools long enough to undergo putrefactive decomposition, and why and how oxidation should be accomplished, and it is chiefly through the revelations of the microscope in the mighty world of microorganisms that this all important knowledge has been given to us.

The science of bacteriology has become to the sanitary engineer, in a certain sense, the most interesting and important of all sciences, though dealing with the most infinitesimal of all known living organisms. Without its aid he has been groping about in darkness. With it he proceeds boldly forward on firm ground to the goal of perfect sanitation.

Fig. 27. Mediaeval Metal Worker

Fig. 27. Mediaeval Metal Worker and Plumber.

From Viollet le Due.

Let us, therefore, go with the biologist into his laboratory for a while and view with him the marvels of the microscopic world, the little beings upon whose activity all life on our planet depends, the agency through which new life returns from death; the silent, untiring builder, infinitesimal and impotent as a single individual, but gigantic and irresistible as a collective force.

The word "bacterum" or "microbe" means to most people, even today, something terrible and destructive, because only within the last few years have we learned the vastly greater importance of these organisms for good than for evil, and see in them our indispensable friends. There are black sheep among them, but they are as few, comparatively, as the criminals in human society who constitute the "rogues' gallery." There is no family of visible plants which begins to compare with these microscopic ones in importance.

Although there are now known to be several hundreds or perhaps even thousands, of different species of bacteria, they have only a few general forms which correspond respectively to spheres, rods, and spirals. Our Fig. 28* illustrates all of these forms. At the top we see in Figs. 1 to. 5 of the plate, the spherical bacteria, called micrococci. Although they all look alike, they are nevertheless all of entirely different species, those in Fig. 2 being disease germs, and the remainder being germs of fermentation. Fig. 6 is a yeast bacterium which forms the beautiful rose-colored patches on cooked potatoes. Next below come the rod formed bacteria, Figs. 8 to 16, some of which are in process of division into shorter pieces, the usual method of multiplication of bacteria. Those in Fig. 10 come from the surface of sour beer. The remaining figures show the spiral bacteria. Fig. 17 is named in this plate as the "vibrio serpens," and Fig. 21 the "spirillum volutans." Fig. 19 the "spirillum tenui," single and felted into "swarms."

•From "The Bacteria," by Dr. Antoine Magnin, translated by Dr. G. M. Sternberg.

Fig. 28. Bacteria.

Fig. 28. Bacteria.

All these organisms are far too minute to be visible to the naked eye. The spheres vary from one to six one-hundred-thousandths of an inch in diameter, and the rods and spirals have a thickness about the same as the diameter of the spheres, and a length varying all the way from a little more than their thickness up to long threads of a thousandth of an inch or more.

Frankland,† speaking, of the size of bacteria, says we could have a population of them one hundred times as great as that of London settled on a single square inch, without any complaint of overcrowding, but giving each individual organism one four-hundred-millionth of a square inch of space, which is quite adequate for a citizen in the commonwealth of these Liliputians.

It is in their enormous and almost incredible power and rapidity of multiplication that their importance lies, some species having been observed under the microscope to divide every half hour or less. They infest all our surroundings, entering our nostrils with every breath we take, swimming in every draught of water, and are in full possession of every inch of ground we stand upon.

They do not, however, descend to very great depths in the soil, few existing, according to Prof. Conn,++ below four feet. At the surface they are very abundant, and if the ground is moist and full of organic material the number may range here from a few hundred to several millions per grain. In the ocean they are found at all depths within a hundred miles from the shore, as well as in the sediment at its bed. At the rate of reproduction observed, each bacterium would have over sixteen million descendants in a clay, and over 281 billion in two days, aggregating in weight about a pound. At the end of the third day, if the process were uninterrupted, the descendants would weigh about 16 million pounds, and in five days they could, if properly nourished, fill the entire Atlantic ocean solid full. Fortunately, however, Nature supplies the bacteria with a number of enemies most wonderfully adjusted to keep them within proper bounds.

†"Our Secret Friends and Foes," by F. F. Frankland. ‡H. W. Conn, "The Story of Germ Life." D. Appleton & Co., N. Y.

Now this marvelous power of growth is chiefly due to a fact which gives the bacteria their extreme importance in Nature, especially to the sanitary engineer. Other plants require simple substances like carbon dioxid (C02) and water for their nourishment, but the bacteria are able to feed upon the complex organic material of animal and plant structure. They tear this structure after death to pieces, chemically speaking, and prepare it for new forms of life. The discovery of the conditions under which this is done is revolutionizing the science of sewage disposal.*