"Pestilences that come bodily, like cholera, are faced and beaten by sanitary measures. Those which come more subtly need for their defeat only a higher detective ability and a closer study of causes, many of which are known, but hidden under the cellars of our houses, and which at last are only preventable by public authority and at public expense in letting out the imprisoned dampness which saturates the earth on which our dwellings are built. Where wood rots, men decay. This is clearly shown in the sanitary map printed in the _Times_. In the great district surrounding Central Park, and which participates in its drainage system, there are no cases. On the whole line of Fifth Avenue there are none. The exempt districts are clearly defined by the character of the soil, drainage, and sewerage, and by the topography, which either has natural or artificial drainage, but most of which is so dry that only surface-water and house-filth--which does not exist in those palaces--can affect the health of the residents. But in the tenement houses and on the made lands where running streams have been filled in and natural springs choked up by earth fillings, diphtheria finds a nidus in which to develop itself. The sanitary map coincides precisely with the topographic map made by Gen. Viele. Where he locates buried springs and water-courses, there we find the plague spots of diphtheria and in the same places, on previous maps prepared by the Board of Health, we find other low types and stealthy diseases, such as typhoid and irruptive fevers, and there we shall find them again when the summer and autumnal pestilences have yielded place to those which belong to the indoor poisoned air in the winter. The experience of other cities, notably London and Dublin, once plague spots and now as healthy as any spot on earth, proves that most of the causations of disease are within the control of the competent sanitary engineer, even in localities crowded beyond American knowledge, and houses built upon soil saturated for centuries with the offal of successive and uncleanly generations. Wet earth, kept wet by the boiling up of imprisoned springs, is a focus of disease. Dry earth is one of the most perfect deodorizers, the best of oxydizers and absorbents, destroying the germs of disease with wonderful certainty. On those two facts rests the theory of public hygiene." DUST AND DISEASE. The air we breathe is heavily loaded with minute particles of floating dust, their presence being revealed only by intense local illumination. Professor Tyndall says: "solar light, in passing through a dark room, reveals its track by illuminating the dust floating in the air. 'The sun,' says Daniel Culverwell, 'discovers atoms, though they be invisible by candle-light, and makes them dance naked in his beams.'"