portion of oxygen to nitrogen would have been much greater than it is. The weight, too, of the atmosphere would have been very materially increased and our coal beds would have proven far vaster than they are.

A very large part of the purification of the early atmosphere we must credit to the mineral world. It markedly diminished the atmospheric weight for us. In the burnt-up rocks of azoic times, calcium and other such elements were left as oxides and hydrates. Now we find them forming mountain chains and immensely deep strata as carbonates, the greatest proportion of their weight having been absorbed from the air. Every bed of limestone, chalk and marble illustrates this point. The quantity of carbonic acid gas these have absorbed from the air is so vast that if released again the world would be no longer fit for us to inhabit. One is almost constrained to believe that in this early absorption of the mineral world can be found a purposive act. It certainly looks as if cons of ages ago the way was being prepared for our advent. Every change led thitherward. Had the mineral world not absorbed the carbon dioxide, but left all the work to the plants, we might have had more oxygen than to-day, but we would likewise have had more pressure. This in turn would have required changes in the structure of our tissues that would have made such life as we now have impossible. At the proper point to save conditions favorable for us the bulk of the rapid absorption of oxygen by minerals was arrested. Had there been produced in the early world twice as much of these oxides and hydrates as there was, they would have stolen all the food from the plants and all the oxygen from us, thus leaving a barren earth. Had there been enough more than at present to have absorbed the gas which the plants used when forming our coal beds, what sort of civilization would have been pos sible to us? As it was, an evenly balanced strain was fixed upon minerals, plants and animals exactly at the point that made possible our present conditions. That matched strain is maintained in its perfection to this day. The number of plants which the earth is now capable of supporting is fixed by the amount of their food present in the air in the form of carbonic acid

gas. The amount of this carbonic acid is kept up to their requirements principally by our fires and the breathing of animals. There are, however, a number of other sources. The fact that this is so shows us that the number of animals upon the earth and their character has a limiting power upon the number of plants, and the number of plants on the other hand limits the number of animals. Any great decrease in the number of plants would lower the oxygen supply that is now but little more than required. Any great decrease in the number of animals would lower the carbonic acid gas supply that is now little, if any, more than required. The quantity of each of these gases remains practically constant from year to year, showing that waste and supply do no more than balSuch oscillations as may exist in favor of one side or the other cannot at present be detected with certainty. The plant world seems to utilize all the carbon dioxide as fast as it is produced, and the animal world all the oxygen; so that the bank account of each as found in the air is neither markedly increased nor diminished except in narrow limits for brief priods of time.

ance.

It is evident, from a survey of the facts already pointed out, that every breathing creature from the first dawn of time, has had to conform its structure to the conditions imposed by the nature of the air supply. The structure of our blood and its chemical composition is such that it can only perform its work properly where there is but little carbon dioxide and much oxygen. The structures of our lungs, hearts, livers and blood vessels are exactly adjusted to such a quality of blood and such air. Through all the countless years of the past every creature in the line of descent toward, ourselves has survived solely because these organs changed as the air changed, thus adapting themselves to the new environment. In every instance where such change did not occur, disease, followed by death, terminated their careers. Even in the slight changes of recent days, failure of adjustment must be leaving its mark. It is certain that slight deviations from the true physiological balance of structure cause certain families to be liable to

certain diseases. We now know that the old notion that consumption is hereditary is wrong. But we also know that a very slight narrowing in the diameter of the pulmonary arteries and veins renders one more liable to consumption. Since some families have a structural deviation of this kind that is hereditary, all such people are more likely to have consumption of the lungs than others. The principal reason lies in the fact that they are unable to as fully aerate their blood and keep it in perfect vigor as their more fortunate fellow creatures. Where such people are constantly engaged in vigorous, healthy out-of-door work, they seldom catch the disease, even, though liable. Of course, if exposed to great changes of weather, out of door work may become the least favorable for them. When compelled to rapidly and completely inflate their lungs by reason of proper physiological exercise, they are safe under otherwise ordinary conditions of exposure to the disease. The causes that conspire to this and other serious forms of disease have been traced to the atmosphere. At one time miasmatic gases were blamed for some maladies, and to this day we hear of people suffering from malaria which when interpreted into plain English means "bad air." It is not the air itself, nor any gaseous constituent thereof, that is directly responsible for these troubles. The part performed by the air in the affair resides in its buoyant property by means of which light particles of solid matter are able to float in it. However pure the atmosphere may seem to be at any time, it is sure to be heavily laden with invisible dust particles. When a bright beam of light is projected into any dark or shady place you are always sure to see a mass of dust that looks as if it might smother us to breathe it. And yet such is the state of the air at all times under the ordinary conditions in which we live. This mass of floating dust we are constantly breathing and swallowing. There is not a spot in our homes or churches, streets or roads, that is not befouled by its presence. This dust is composed of the worn-out threads of our garments, the dried epithelium from our bodies, mineral particles from our walls, andthe ground, decomposed material from our lungs and mouths, pollen from

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plants, spores from moulds, and worst of all, disease germs from infected soils and swamps, from dried-up sputa of consumptives and from the breath of people who walk our streets suffering from what to them with their resisting powers are merely slight ailments but to others is certain death. Go where we will we cannot escape. Air we must have, poisoned or pure, and it is always poisoned in some degree. That it has been ever so we have every reason for believing. to the present time, only creatures capable of resisting these invisible foes, that the air is the innocent means of carrying around, have survived. Whenever, in the past, a new germ appeared in a region and among people not able to resist it, they have perished by thousands, and history mentions the circumstance as a plague or pestilence. Subsequent attacks have usually been milder because the susceptible were nearly all killed before. When, however, physical filth or moral impurity has lowered the vital resistance of a people, even this rule of immunity does not hold good. We have also reasons for believing that such filth and such impurity render more vigorous the germs themselves, so that they can attack people who otherwise might, under ordinary circumstances, have escaped.

Nature thus holds us responsible not only for our own short-comings, but for those of our neighbors as well. As the best built fire-proof granite buildings melted before such a fire as Chicago witnessed, and more readily because many had been so imprudent as to put mansard roofs over their houses, so the strongest constitution is swept down by germs that are multiplied in numbers and virulence by the crimes of the filthy. Nature therefore declares that we are all our brothers' keepers, since their lives depend upon our deeds, and vice versa. These germs that under ordinary circumstances are unable to attack us, may by reason of our violating some law of nature and weakening our vitality, instantly find a home in our flesh, where they will live and multiply like weeds in a garden. If we get chilled beyond our margin of endurance they instantly begin to grow on our tongues, in our stomachs, in our intestines, in our lungs or in our blood. Then we have coryza, or dyspepsia, or rheu

matism, or pneumonia, or pleurisy. But for that chilling they would have passed through us and been unable to get a foothold, since the strength of our cells would have been more than a match for them. If we get overheated, a similar train of maladies may arise. If we have overworked, that lowers the vital powers. Intoxication, loss of sleep, gluttony and excesses of every kind lay us liable to their attack by weakening the constitution and therefore its power of resistance. We are thus admonished of the fact that Nature is the relentless foe of every form of intemperance, and that the wages of all such sin is death. We see that not only our own sins but the sins of our fellows are charged up to us. In this we discover the duty that is imposed upon us to work for the elevation of the whole human family and its reclamation from filth, ignorance and crime. To live where wickedness rules is to suffer from it, although we may try ever so hard to escape its consequences. To tolerate ignorance of hygienic laws among our fellows is to endanger our own lives and the lives of our friends. An apt illus. tration of this is seen in the great prevalence of tuberculosis. This disease kills about one-ninth of our race, and its main source of propagation we make no effort to check. Consumptives are allowed to spit where and when they please, notwithstanding the fact that their spittle is death laden for millions. It dries on the ground, floats in the air and is breathed in by others who die from such carelessness.

The diminished density of our present atmosphere as compared with that of primitive times gives it a very greatly reduced capacity for floating dust particles and germs. Its dangerous qualities then as compared with the present were therefore greater in this particular as well as in that of being laden with mephitic gas. During all the intervening years, the acquisition of immunity from certain kinds of disease-germs had been acquired. It is a remarkable fact that of the hundreds of known species of micro-organisms only a very few are pathogenetic. Whether this is due to an acquired immunity or not, of course no one can tell; but the existence of such a fact is significant. They are all capable of growing on dead animal-or