of doors. The quantity of water required for saturation of the air differs with the temperature. Air at 66 degrees requires 6 grains of water in each cubic foot, but air at 30 degrees holds only 2 grains; consequently, if air be reduced from 66 degrees to 30 degrees, it parts with 4 grains of its moisture per cubic foot, in the form of dew; if then it be afterwards raised again to 65 degrees, without more water being supplied, it must necessarily feel dry and harsh. Hence, if in winter, by the warming apparatus, we raise the temperature of the air from 32 degrees to 65 degrees, we must supply it with water; otherwise it must necessarily be disagreeable and unhealthy, because of its rapid abstraction of moisture from the lungs and skin.

Having thus shown the necessity, in general, of providing pure air for all citizens of a Commonwealth, I shall now proceed to examine the conditions which are by no means so few as may appear on a superficial examination under which alone this can be done.

To provide pure air for every person, and thus protect each from the contaminating influences of all kinds of miasmatic and other impurities, the legislative power in each State must regulate

1. The laying out of cities and villages in such a manner as to make possible the needful ventilation of their buildings, and the providing of public drainage.

2. The construction of all private as well as public buildings in such a manner as to make accessible to every inmate the necessary quantity of pure air, and the establishing of private drainage.

3. Personal cleanliness.

4. The laying out of counties and townships.

But, before entering into details, let me cite a few touching passages from Dickens's famous Dombey and Son:

"Breathe the polluted air, foul with every impurity that is poisonous to health and life; and have every sense, conferred upon our race for its delight and happiness, offended, sickened, and disgusted, and made a channel by which misery and death alone can enter. Vainly attempt to think of any simple plant, or flower, or wholesome weed, that, set in this fœtid bed, could have its natural growth, or put its little leaves forth to the sun, as God designed it. And then, calling up some ghastly child, with stunted form and wicked face, hold forth on its unnatural sinfulness, and lament its being, so early,

far

from heaven, away but think a little of its having been conceived, and born, and bred in hell!

"Those who study the physical sciences, and bring them to bear upon the health of man, tell us, that if the noxious particles that rise from vitiated air were palpable to the sight, that we should see them lowering in a dense, black cloud above such haunts, and rolling slowly on to corrupt the better portion of a town. But if the moral pestilence that rises with them, and in the eternal laws of outraged nature is inseparable from them, could be made discoverable too, how terrible the revelation! Then should we see depravity, impiety, drunkenness, theft, murder, and a long train of nameless sins against the natural affections and repulsions of mankind, overhanging the devoted spots, and creeping on to blight the innocent and spread contagion among the pure. Then should we see how the same poisoned fountains that flow into our hospitals and lazar-houses, inundate the jails, and make the convict-ships swim deep and roll across the seas, and overrun vast continents with crime. Then should we stand appalled, to know that where we generate disease to strike our children down and entail itself in unborn generations, there also we breed, by the same certain process, infancy that knows no innocence, youth without modesty or shame, maturity that is mature in nothing but in suffering and in guilt, blasted old age that is a scandal on the form we bear. Unnatural humanity! When we shall gather grapes from thorns, and figs from thistles; when fields of grain shall spring up from offal in the by-ways of our wicked cities, and roses bloom in the fat church-yards that they cherish, then we may look for natural humanity and find it growing from such seed."

CHAPTER IV.

LAYING OUT OF CITIES.

The laying out of cities according to principles of sanitary science is practicable only, of course, in new cities, or in new additions to cities already existing, though it may in many cases be possible also

to rebuild old and badly built cities on a sanitary plan, at least in part; as Paris, for instance, was remodelled. Large fires and other circumstances may also make such reforms practicable in many cities.

In this matter it is first of all necessary, that the State should determine and establish for all cities and villages the minimum width of boulevards, streets, and alleys, and the proportionate number of open public squares. In my judgment, every fourth street should be a boulevard, and every fourth square in every direction would constitute the proper proportion of public squares. At least a part of these squares, and the centre and side lines of the boulevards also, should be planted with trees, to absorb the carbonic acid gas with which the air of a crowded city is always surcharged, and to furnish shade for the inhabitants.

Indeed, the value of trees for purifying the air, in large cities especially, can scarcely be overestimated. Their influence as such purifying agents is, indeed, almost incredible. Take into calculation, for instance, that a fair-sized elm, plane, or lime-tree will produce seven hundred thousand leaves, with an area of two hundred thousand square feet. Now, all these leaves greedily absorb the carbonic acid of the atmosphere, which to animal life is simply poison, and having absorbed it, breathe it forth again as oxygen. At the same time they thereby modify the temperature, promoting coolness in the summer and furnishing warmth in winter; while the trunks of the trees materially assist sewerage in purifying the soil.

I may add, that the same principle of purifying the air holds good in regard to house-plants. I quote from a celebrated authority, Dr. J. M. Anders, of Philadelphia:

"The average rate of transpiration for plants having thin, soft leaves, like geranium, lantanas, etc., is found to be an ounce and a half of watery vapor per square foot of leaf-surface for twelve diurnal hours of clear weather. At this rate, a great tree like the Washington Elm at Cambridge, which has been estimated to have two hundred thousand square feet of leaf-surface, would exhale seven and three-fourths tons of water in twelve hours. The rate of transpiration for a house-plant is at least fifty per cent more rapid than for one in the open air; and it is evident, on the face of it, that a number of such plants must have a material influence upon the humidity of the air in which they are kept.

"By means of the hydrometer, the atmosphere of two rooms at the Episcopal Hospital, in which the conditions and dimensions were in every respect similar, were tested simultaneously, in order to note the variations produced by growing plants. In the window of one of the rooms were situated five thrifty plants; the other contained none. For eighteen consecutive days the dew-point of the room containing the plants gave an average complement one and a half degrees lower than the room in which there were no plants.

"To make it sure that the difference in humidity was due solely to the presence of the plants, the conditions were varied and further observations made, but the results were similar.

"Since it is well known that certain maladies - especially those affecting the lungs and air-passages are benefited by a moderately moist and warm atmosphere, and since plants furnish moisture to the warm air of a dwelling, these may properly be classed as therapeutic agents.

"The plants should be well selected, and kept in a thriving condition. The chief point to be borne in mind in the selection of the plants are, first: that they have soft, thin leaves; secondly: foliage plants, or those having extensive leaf-surface, are to be preferred; thirdly those which are highly scented (as the tuberose, etc.) should be avoided, because they often give rise to headache and other unpleasant symptoms.

"In order to facilitate a practical application of the data gained by experiment, the following formula has been carefully prepared: Given a room twenty feet long, twelve feet wide, and ceiling twelve feet high, warmed by dry air; a dozen thrifty plants, with soft, thin leaves, and a leaf-surface of six square feet each, would, if well watered, and so situated as to receive the direct rays of the sun (preferably the morning sun) for at least several hours, raise the proportion of aqueous vapor to about the health standard.

"To obtain the best results, both the rooms occupied during the day and the sleeping-apartments should contain plants. It was for a long time the opinion of scientific interpreters generally, that plants in sleeping-apartments were unwholesome, because of their giving off carbonic acid gas at night; but it has been shown by experiment, that it would require twenty thrifty plants to produce an amount of the gas equivalent to that inhaled by one baby sleeper; so that is no

valid objection to their admission, and not to be compared with the benefit arising from their presence."

But there is another way in which trees and plants act directly upon the human body, and purify the air which has been contaminated by its exhalations; for our own bodies inhale and exhale electricity, like the earth or the air. It has been calculated that the watery vapor which in the course of twenty-four hours exhales from the surface of a healthy body amounts to from thirty to forty ounces of water. This is sufficient to disturb the electric equilibrium of the body, and to evolve electricity of much higher tension than that set free by chemical action. This evaporation may probably account for the traces of free electricity generally to be detected in the body, by merely insulating a person and placing him in contact with a condensing electrometer. Pfaff and Ahrens generally found the electricity of the body thus examined to be positive, especially when the circulation had been excited by partaking of alcoholic stimulants. Hummer, another observer, found that in 2,422 experiments on himself, his body was positively electric in 1,252, negative in 771, and neutral in 399. The causes of the variations in the character of the electric conditions of the body admit of ready explanations in the varying composition of the perspired fluid. For if it contains, as it generally does, some free acid, it, by its evaporation, would leave the body positively electric; while if it merely contains neutral salt, it would induce an opposite condition. The accuracy of these statements can be easily verified by means of the electrometer.

But perhaps the most astounding feature of modern scientific discoveries is the reciprocal influence of electricity on plants. I have already explained the vast benefits which result from the exhalation of ozone, or electric oxygen, by flowers. And now Dr. C. W. Siemens, in a report to the Royal Society of Physical Science, in London, makes the announcement: that plants shut up in a closed room, if lighted by electric light, flourish quite as well as those exposed to sunlight.

To substantiate his statement, he exhibited tulip buds, and placing them under the influence of electric light forty minutes, brought them forth before the eyes of his spectators full-grown flowers. Mustard, bean, cucumber, melon, and other quick-growing seeds developed in the same proportion.

It thus appears clearly, that electric light, if properly applied, can