[53] Ozone is said to oxidize the poison. It destroys sulphuretted hydrogen and all oxydable miasms, and is the most powerful disinfecting agent, but is itself unfit for respiration: it causes suffocation. Air in its normal state contains one ten-thousandth part of ozone; when raised to one two-thousandth part it is sufficient to kill small animals.
[54] Hydrogen, or inflammable air, is the lightest known substance; its specific gravity is to that of air as 732 to 1000. The gases, into the composition of which it enters, rising from these ditches and banks of mud carry with them dried humus, and even animal matter in a state of putrefaction, which, being dry or moist, may act as strongly as variola itself, in respect of its injurious effects on man, who breathes it either as it rises from ditches, or is driven by currents of air circulating round watery places covered with humus. It is even (onctueux) so strong that it will sustain seeds and dust upon water, as I have witnessed at Amsterdam, Rotterdam, Verona, Bologna, Venice, and even in the canals of Lambeth and Deptford. By means of hydrogen we raise a balloon; can we not imagine it to be equal to the raising up of humus? It is generally supposed that sulphuretted hydrogen is amongst the dangerous miasms, but it cannot be so hurtful, for no boat can go into canals without disturbing it, and yet we see no evil results from this; but if the water-level lowers, and leaves vegetable or animal matter upon mud in a state of slow combustion, then it is that fevers commence—a fact, I think, I have proved by an appeal to the history of pestilences in ancient and modern times.
[55] “Decline and Fall,” vol. iii. p. 391, Milman’s edition.
[56] The idea of employing the drainage of towns, partaking under all circumstances more or less of the nature of sewage—using the term in its most extensive sense, as comprising the excreta of the entire population—seems first to have originated in Scotland, and especially in the vicinity of the capital. The period is perhaps not well known, but about the commencement of the present century we find the system in full force, but limited to the great outlets of the drainage and soiled water of the town. These great drains were not strictly speaking sewers, but drains, for at that time there were but few sewers, properly so called. If cesspools existed, they were not emptied into the drains, or so-called town-sewers, so that the matters contained in the two great outlets used for the purposes of foul-water irrigation bore little or no resemblance to the turbid, frightful, and most putrescent mass now conveyed into the Thames by the sewers of London. This essential distinction in the quality of the material has been ignored or passed over in the Reports of the Board of Health. Not that the irrigating water was to be considered as pure; on the contrary, it was extremely filthy; but it did not at that time contain the sewage of the town, properly speaking. It probably now does so in consequence of the extension of the system of water-closets, latrines, &c. The Scotch agriculturists who employed the water of these vast foul drains, would have much preferred pure water, but they had it not at their command. With this, such as it was, they irrigated certain tracts of land, some of which were originally barren wastes, converting them into meadows on which grew a peculiar kind of grass, which cattle (milch cows) do not reject after having been accustomed to its use. But the farmers knew well that the abominable liquid they thus poured over their fields was wholly unfit for the usual agricultural purposes; and thus in no instance did they employ it as manure. The Grange drain was used by one market-gardener only, simply for the purposes of irrigation during droughts, but not with any view to the manuring of the garden. By the time that all the cesspools of London have been poured into the drains, and the system of drainage and sewage completed and formed into one system, there arises the question as to how the material is to be disposed of? The pouring it into the Thames at a point below the influence of the tide is perhaps, after all, the easiest and least expensive mode of escaping from the dilemma into which the capital has been brought by the clumsy experiments of the late Board of Health; but what the ultimate result of this additional experiment may be, no one can foretel. If transmitted to the fields, the farmers are sure to reject it as manure; but it might be conveyed to barren waste lands, mere sandy wastes, the qualities of which no doubt in time it would beneficially affect, converting them first into meadows, and possibly afterwards into land favourable for the growth of certain green crops. The liquid might also be conveyed to estuaries which it might be desirable to fill up, and the numerous small tidal harbours which the extension of railways will speedily render of little or no value to the inhabitants.
The mud deposited in tidal harbours or on the banks of rivers within the influence of the tide is of no value as a manure; when spread over the fields, the result is the loss of the crops for some years.
[57] Gibbon.
[58] Niebuhr.
[59] Extremique hominum, Morini Rhenusque bicornis. Æneid viii.
[60] “Ab urbe condita;” from the building of the city (Rome), the era fixed on by the Romans.
[61] This question was first agitated in the reign of Justinian, on the occasion of a proposal on his part to form a treaty with the negroes of Abyssinia. But the Abyssinians were not negroes.