may further, in waters subject to sewage contamination, become the source of serious danger. In any case, enough is now known to justify us in saying that we need to know more. The importance to the health of the communities of a complete knowledge of everything affecting water-supplies, is so evident that there seems to be no question as to the desirability of fully informing ourselves about the natural causes of deterioration which are liable to occur to watersupplies.

THE RELATION OF GROUND-WATER TO THE

HEALTH OF THE COMMUNITY.

BY COL. GEORGE E. WARING, JR.

Nearly every community, in all countries, lives on a soil which, below a certain depth, is saturated with water. This sometimes very near to the surface, sometimes very deep below it; sometimes nearly quiescent, and sometimes in active movement; sometimes subject to marked rise and fall under the influence of rain and drought, sometimes practically uniform in its elevation. Sometimes it is subject to the action of rising and falling tides, even though its level is considerably higher than that of the tide-water, and the distance somewhat remote.

I have said that this water is sometimes nearly quiescent; it is never entirely so. In some form or other, it is receiving additions, and, either by evaporation or by leakage, it is undergoing waste. Following its tendency to maintain its level, waste at any point must be supplied by a flow from other points and an addition at any point must be equalized by a flow toward other points. Sometimes rims of elevated clay or rock maintain in the soil something approaching the conditions produced by a mill-dam, holding the line of saturation at a given elevation, which, however, in this case is rarely a level, because of the tendency to loss by evaporation or leakage at one part more than at another, and because of an inflow from outlying sources. As a rule, rivers are fed chiefly by underground flow. During heavy rains, a portion of the downfall flows off over the surface and goes directly to the river. Most of it enters the ground, raises the level of its water of saturation, forcing it forward toward the nearest drainage line, whether brook, creek or river. Where the flow toward these drainage lines is considerable, the water in the soil is always higher, sometimes materially higher, than the water of the river, save only when the latter shall have been temporarily raised by an

inflow of surface-water. It requires a certain amount of extra elevation, or head, to force the water forward toward the river in order to overcome the friction of the particles of earth among which it is flowing. In coarse gravel this difference of head may not amount to much, but as the obstructing particles become finer, increasing the frictional surface and reducing the size of the space through which the water must run, more and more head is required to produce the discharge. If the discharge is into water of permanent level, the depth of the water from the surface at any given point may remain approximately the same, but if the discharge is into a contiguous body of water subject to a strong tidal rise and fall, the elevation of the ground-water for some distance back from the shore will be subject to corresponding fluctuations. Although the level of the ground-water may be some feet higher than the highest high tide, it will fall somewhat as the tide falls and will rise somewhat as the tide rises, even although its lowest surface elevation during low tides may never run so low as the level of the highest tides.

Fifty years ago a knowledge of the laws governing the existence and movement of ground-water had little practical interest save as they related to the digging of wells, unless, indeed, the water rose so high as to invade cellars or to saturate porous foundation walls. Now the case is greatly altered. While we have yet a vast deal to learn as to the sanitary bearings of ground-water, and especially as to the relations of the rise and fall of this water to the production or fostering of certain epidemics, we have learned enough to know that either in this water or in the ground's breathing space between the surface of the water and the open air, we have to look for some of the most serious dangers that beset us, and that the whole question of sanitary drainage, the purification of sewage and the lessening of malaria must here seek its most important solution.

Nothing that may be said in a discussion of this sort concerning the character, habits of life and sanitary relation of those microscopic forms of life which now engage so much of the attention of the biologist is to be accepted as a scientific statement; indeed, it is difficult to say where, in the professional pursuit of bacteriology, the line between science and speculation lies. At the same time, enough has been demonstrated to show that certain grave, and in some cases fatal, diseases-the chief scourges of the human race, the sources of suffering, inefficiency and depression, as well as of death-are fostered and

transmitted, and are often given epidemic proportions, through the development of microscopic forms of life. If we err at all, we shall err on the safe side in assuming that there is no longer a question as to the relation between these microscopic germs and our most serious diseases. No more than in a discussion as to the origin of these germs are we able to say with scientific accuracy what are the conditions most favorable to their development or to their destruction. But we may safely assume that the water of the soil and the condition of the breathing space above that water may have, and under certain conditions do have, a very marked influence on the character and development of disease-producing organisms and on the opportunities for their reaching and infecting the human subject.

Whether or not all or most of the disease-producing microbes can escape from the soil into the air, under natural conditions, it seems clear that at least the causative microbe of malarial fever does so. The probability is that most of the pathogenic microbes in the soil are conveyed to their field of operation in the human system in drinking-water, sometimes by a flow of polluted ground-water into wells and sometimes by its flow into small streams from which drinking-water is obtained. That infection may be communicated by ground-water has been proved beyond question. The degree to which infection may be carried through a soil of ordinary consistency has not been determined, but the probabilities are that unless there are sand or gravel strata, or rock fissures, carrying the stream faster than it can be filtered, infection will not follow the flow.

Whether or not ground-water containing slight organic impurities can serve as a breeding medium for microbes, has not been determined. That it does form a field for their multiplication when accumulated in wells, there cannot be much doubt. The one undeniable conclusion that must be drawn, a conclusion forming one of the fundamental bases of sanitary hypotheses, is that polluted water in the ground is always liable to produce disease among those living over that ground, whether they breathe its exhalations as drawn into cellars, when the surface is frozen, and the breathing space of the soil becomes a source of the draft of chimneys, or drink water drawn from the subterranean supply. The unquestionable result from this is that there can be no absolute safety short of securing absolute purity of the ground-water, so far as organic matter is concerned. This implies, of course, the purity of the soil itself.

If we discharge filth through leaking sewers, or by soaking from leaching cesspools, or from the deposit of organic wastes or of dead bodies below a certain depth from the surface, we are endangering the purity of the soil itself, and especially of the water flowing through or standing in it. Here lies the most obvious and direct relation between ground-water and the health of the community. The water is probably to be regarded as a field for the multiplication of microbes, and it is surely to be regarded as a means for the transportation of these from one point to another, when its movement is not obstructed by a fine soil of measurably uniform texture. These effects, indeed, belong to elementary knowledge of the subject, and are familiar to all who have given even casual attention to it.

There is one condition, however, which is not so generally understood, but which seems to be clearly established. This is that it makes a very great difference whether the organic matter reaching the soil is introduced into it at or near the surface, or at a considerable depth. A discussion as to what takes place in the decomposition of organic matter under different circumstances is rather delicate ground, but the following may be accepted either as being correct, or as indicating results which are produced by some other process than the one indicated. This theory is that the putrefaction of organic matter and the nitrification of the products of putrefaction are due to specific organisms which have the power to destroy, not only the organic matter itself, but also those specific microbes which produce infection; also that these putrefying and nitrifying organisms can grow and multiply only with a sufficiently free access of air. Searches made for them at various depths seem to have established the fact that while in ordinary soil they are excessively abundant within a few inches of the surface, they are excessively rare at a depth of two feet, and that they disappear entirely at a slightly greater depth. It is probable, however, that they are capable of descending as far as their pabulum can be carried by direct progression from the surface, provided a sufficient supply of air can reach the same depth; so that if we thoroughly underdrain a piece of porous ground and dose it heavily with sewage, the water descending through the soil will deposit its impurities to a greater and greater depth, and, as the condition of saturation ceases, after the temporary application, air from the surface will take the place of the water and establish colonies of microbes at increasing depths.