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THE PROCESSES EMPLOYED IN THE

follow the occupation for many years; and some who are known to us as having had noother employment for more than twenty years, will bear a fair comparison with any of themechanics or labourers of the same ages and living in the same localities.

Nothing is more difficult than to make some people understand, and especially those whointerest themselves in sanitary measures, that what are called offensive odours are not neces-sarily injurious. On this subject the opinion which generally prevails is that disagreeable andunwholesome are, in almost every instance, synonymous,—that whatever is repugnant to oneof the senses (smell) is likely to endanger the health of the whole body. It is not so. Webelieve it to be well deserving of consideration, whether there is any evidence whatever thata purely gaseous body ever generates disease. It is far more probable that miasma is vapourthan that it is gas* The gases evolved from sewers, drains, cesspools, and other sources ofpollution, are mechanically mixed with vapour; and the gases by their elasticity, by theirhabit of diffusing themselves the instant they escape from their prison-houses, and by theircapacity, according to temperature, for absorbing and carrying moisture about with them, areundoubtedly the means by which the poisonous organic compounds, resulting from the de-composition of vegetable and animal substances, are distributed and diluted. But the vapo-rized organic matter here referred to is no more entitled to the name of gas, than the vapourwhich in variable quantities is always present in the atmosphere, is to that of air. Theoffensive odours of the gases just mentioned are probably to be reckoned among their mostimportant properties. By appealing so quickly to one of the most sensitive of our organsthey warn us of danger.

In the manufacture of coal-gas, great quantities of sulphuretted hydrogen (hydro-sulphuricacid) are produced. When permitted to escape into the atmosphere, it is soon recognizedby its characteristic odour; its pungency and tendency to diffuse itself being increased byammonia, with which, in the process of purifying, it readily combines and forms hydro-sul-phuret of ammonia. But although many of the men employed in gas-works inhale in anhour greater quantities of what are commonly considered to be deleterious gases than any ofthe inhabitants of the filthiest districts in the kingdom are likely to do in a week or a month,they are not in the slightest degree affected thereby in their general health. The specificeffects of these gases on the respiratory organs and the brain, when insufficiently diluted,are in no respect doubted or disputed. These are not the conditions in which, under ordi-nary circumstances, they present themselves within and around a gas establishment. The

* In some experiments conducted by Mr. Lewis Thompson, and noticed at length in the second volumeof the ‘Journal of Gas Lighting,’ it was ascertained that the condensed vapour collected in the wards of anhospital and in a sewer, after being kept for some hours in a warm temperature, and then examined by themicroscope, exhibited a number of confervous plants and infusorial insects. These organic substances werenot perceptible in the condensed vapour collected in salubrious places, though the chemical constituents ofthe air were in all cases the same. Mr. Thompson also found that the condensed vapour of infected placeswhen a single drop of coal-tar water, camphor water, or water mingled with the oil of cloves was added toit, afterwards gave no indications of vitalized structures. This seems to show, he observes, “that the variousforms of volatile hydro-carbons exercise a beneficial action, and it is probable that the large amount ofvolatile oil continuously dissipated during the warmer months of the year from flowers and plants is a pro-vident arrangement of the Creator for correcting what may, after all, prove to be the origin of pestilence.”