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"3. The evaporation of the surplas moisture lowers the "temperature, produces chills, and creates or aggravates "the sudden and injurious changes or fluctuations by "which health is injured."

In view of the foregoing opinions as to the cause of ma laria, and of the evidence as to the effect of draining in removing the unhealthy condition in which those causes originate, it is not too much to say that,-in addition to the capital effect of draining on the productive capacity of the land,--the most beneficial sanitary results may be con fidently expected from the extension of the practice, espe cially in such localities as are now unsafe, or at least undesirable for residence.

In proportion to the completeness and efficiency of the means for the removal of surplus water from the soil:-in proportion, that is, to the degree in which the improved tile drainage described in these pages is adopted,-will be the completeness of the removal of the causes of disease. So far as the drying of malarious lands is concerned, it is only necessary to construct drains in precisely the same manner as for agricultural improvement.

The removal of the waste of houses, and of other filth, will be considered in the next chapter.

NOTE. (Third edition.) No practical result has ever come of the researches of Dr. Salisbury described in this chapter, but his investigation followed with curious closeness the path through which later explorers-Pasteur, Koch, and others have reached their remarkable identification of microscopic organisms as the means of contagion of a number of serious diseases of men and animals.

CHAPTER XI.

HOUSE DRAINAGE AND TOWN SEWERAGE IN THEIR RELATIONS TO THE PUBLIC HEALTH.

The following is extracted from a report made by the General Board of Health to the British Parliament, concerning the administration of the Public Health Act and the Nuisances Removal and Diseases Prevention Acts from 1848 to 1854.

"Where instances have been favorable for definite ob"servation, as in broad blocks of buildings, the effects of "sanitary improvement have been already manifested to an "extent greater than could have been anticipated, and than can be readily credited by those who have not paid atten"tion to the subject.

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"In one favorable instance, that of between 600 and 700 persons of the working class in the metropolis, during a 66 period of three years, the average rate of mortality has "been reduced to between 13 and 14 in 1000. In another "instance, for a shorter period, among 500 persons, the mortality has been reduced as low as even 7 in 1000. "The average rate of mortality for the whole metropolis "being 23 in 1000.

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"In another instance, the abolishing of cess-pools and "their replacement by water-closets, together with the "abolishing of brick drains and their replacement by im

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permeable and self-cleansing stone-ware pipes, has been "attended with an immediate and extraordinary reduction "of mortality. Thus, in Lambeth Square, occupied by a "superior class of operatives, in the receipt of high wages, "the deaths, which in ordinary times were above the gen66 eral average, or more than 30 in 1000, had risen to a rate "of 55 in 1000. By the abolishing of cess-pools, which 16 were within the houses, and the substitution of water"closets, and with the introduction of tubular, self-cleansing "house-drains, the mortality has been reduced to 13 in 1000.

"The reduction of the mortality was effected precisely among the same occupants, without any change in their "habits whatever."

"Sewers are less important than the House-Drains and "Water-Closets, and if not carrying much water, may be "come cess-pools. In the case of the Square just referred "to, when cess-pools and drains of deposit were removed "without any alteration whatever in the adjacent sewers, "fevers disappeared from house to house, as these recep"tacles were filled up, and the water closet apparatus substituted, merely in consequence of the removal of the de"composing matter from beneath the houses to a distant "sewer of deposit or open water course.

"If the mortality were at the same rate as in the model "dwellings, or in the improved dwellings in Lambeth "Square, the annual deaths for the whole of the metropolis "would be 25,000 less, and for the whole of England and "Wales 170,000 less than the actual deaths.

"If the reduced rate of mortality in these dwellings "should continue, and there appears to be no reason to 66 suppose that it will not, the extension to all towns which "have been affected, of the improvements which have been "applied in these buildings, would raise the average age "at death to about forty-eight instead of twenty-nine, the 66 present average age at death of the inhabitants of towns "in all England and Wales,”

The branch of the Art of Drainage which relates to the removal of the focal and other refuse wastes of the population of towns, is quite different from that which has been described in the preceding pages, as applicable to the agri. cultural and sanitary improvement of lands under cultivation, and of suburban districts. Still, the fact that town and house drainage affords a means for the preservation of valuable manures, justifies its discussion in an agricultural work, and "draining for health" would stop far short of completeness were no attention paid to the removal of the cause of diseases, which are far more fatal than those that originate in an undrained condition of the soil.

The extent to which these diseases, (of which typhoid fever is a type,) are prevented by sanitary drainage, is strikingly shown in the extract which commences this chapter. Since the experience to which this report refers, it has been found that the most fatal epidemics of the lower portions of London originated in the choked condition of the street sewers, whose general character, as well as the plan of improvement adopted are described in the following "Extracts from the Report of the Metropolitan Board of Works," made in 1866.

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"The main sewers discharged their whole contents di'rect into the Thames, the majority of them capable of "being emptied only at the time of low water; conse "quently, as the tide rose, the outlets of the sewers were closed, and the sewage was dammed back, and became 'stagnant; the sewage and impure waters were also 'constantly flowing from the higher grounds, in some in'stances during 18 out of the 24 hours, and thus the thick 'and heavy substances were deposited, which had to be afterwards removed by the costly process of hand labor. "During long continued or copious falls of rain, more par "ticularly when these occurred at the time of high water "in the river, the closed outlets not having sufficient storage capacity to receive the increased volume of sewage,

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"the houses and premises in the low lying districts, espec"ially on the south side of the river, became flooded by "the sewage rising through the house drains, and so con"tinued until the tide had receded sufficiently to afford a 66 vent for the pent-up waters, when the sewage floweu "and deposited itself along the banks of the river, evolv. "ing gases of a foul and offensive character.

"This state of things had a most injurious effect upon "the condition of the Thames; for not only was the sew 66 age carried up the river by the rising tide, at a time "when the volume of pure water was at its minimum, and 66 quite insufficient to dilute and disinfect it, but it was "brought back again into the heart of the metropolis, there "to mix with each day's fresh supply, until the gradual "progress towards the sea of many day's accumulation "could be plainly discerned; the result being that the por ❝tion of the river within the metropolitan district became "scarcely less impure and offensive than the foulest of the sewers themselves.

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"The Board, by the system they have adopted, have "sought to abolish the evils which hitherto existed, by "constructing new lines of sewers, laid in a direction at "right angles to that of the existing sewers, and a little "below their levels, so as to intercept their contents and 66 convey them to an outfall, on the north side of the Thames "about 11 miles, and on the south side about 14 miles, "below London Bridge. By this arrangement as large a "proportion of the sewage as practicable is carried away "by gravitation, and a constant discharge for the remain"der is provided by means of pumping. At the outlets, "the sewage is delivered into reservoirs situate on the "banks of the Thames, and placed at such levels as enable "them to discharge into the river at or about the time of "high water. The sewage thus becomes not only at once diluted by the large volume of water in the river at "the time of high water, but is also carried by the ebb

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