degree to the completely successful result of the treat

ment.

The smoke, pyroligneous acid, and other perceptible and in general offensive matters, which, as well as carbonic acid, proceed from the burning of most other combustibles, not only prevent their giving rise to the fatally insidious production of this gas, but are, in most cases, insuperable objections to their being burnt like charcoal, in situations in which danger could arise.

Effects similar to those occasioned by the burning of charcoal may be produced by the fermentation of beer and other liquors; and from the same cause, viz. the formation of carbonic acid. I once knew a lady, who being under the necessity of destroying a favourite lap-dog, had it drowned in this gas, by suspending it in a vat over working beer. Brewers themselves have, I believe, fallen a sacrifice in the same way, by desending into their vats, unconscious of the presence of this invisible poison.

Some soils pour out this gas; and if circumstances favour its accumulation, fatal accidents may occur. A curious, rather than dangerous example of the collection of carbonic acid, from this source, is seen in the far-famed Grotto del Cane. Near the floor of this little grotto or cave, the carbonic acid exists in sufficient quantity to prove quickly fatal to dogs taken into it but at a few feet from the ground this effect is not produced; hence, men enter without danger, and can only perceive the presence of the gas by stooping. I did so, when I visited this grotto; and felt the same stinging sensation in the nose which is excited by placing the head over working beer, or drinking a glass of sparkling cider. The choke-damp, so dan

gerous an enemy to our coal-miners, is a more serious instance of the evolution of carbonic acid from the earth. It is well for every one to be aware of two or three facts connected with this gas; viz. that it is heavier than common air, and consequently, like water, seeks the lowest place, and that it instantly extinguishes flame. Its presence may thus be easily detected; and should always be sought for, as a matter of precaution, by those who are about to enter mines, or other subterraneous chambers. When discovered, it may often be absorbed by quick-lime, when it cannot be drawn off, or dissipated by ventilation.

III.

There are other gases, which may be mixed with the air, and produce dangerous and fatal effects. Of these, sulphuretted hydrogen is the most important. It is to this gas that rotten eggs, soap-boilers' lees, and many of the fœtid mineral waters, owe their insufferably offensive odour. Undiluted, this gas is one of the most active poisons with which we are acquainted. I have seen a bird introduced into a receiver containing sulphuretted hydrogen, and in the twinkling of an eye it was dead. It is but a few years since a lady lost her life, in Paris, by going into a bath artificially charged with this gas.

Sulphuretted hydrogen is copiously produced by the putrefaction of animal matters: hence its presence in cesspools, drains, and sewers, and the fatal accidents which have repeatedly occurred from exposure to the air of these places. A less abundant mixture of this gas, though not absolutely fatal, must nevertheless be very injurious. Many are the pernicious effects arising from defective draining; and not the

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least of these may be ascribed to the gas of which I am speaking. In some districts, remarkable for the pernicious fevers to which they give birth, this gas is so abundant, that silver is quickly tarnished by it. Medical men engaged in extensive practice in this city and its neighbourhood have remarked the much more frequent occurrence of fever in some situations than in others; and they have noticed that these unhealthy spots are precisely those in which imperfect draining allows the air to be loaded with offensive effluvia. A fever of a serious character extensively prevailed in one of the largest establishments in the neighbourhood of Paris, and was apparently, with good reason, attributed to the effluvia of a large open drain which passed close to the premises.

Other poisons besides any of the known gases may be mixed with the air, and render it productive of disease. Our noses convince us that different substances, such as musk and asafoetida, may be dissolved in the air. This is the case with the seeds of many diseases. Hence they often affect great numbers of persons in the same place, and at the same time. They seem to be generated by excrementitious matter of every description thrown off from the body, and also by many other species of filth. The fact, that such matters in the worst state are frequently collected without producing immediately perceptible mischief, is no proof that they are innocent. Certain states of the atmosphere, such as complete and continued calm, greatly promote the operation of these poisons, by favouring their accumulation; whilst an opposite state dissipates and counteracts them. Moreover, sudden changes of temperature, and various debilitating causes, acting generally on the inhabi

tants, may concur to promote the prevalence of disease, by increasing their liability to it. When we consider how large a portion of the divine moral law relates to our duty to our neighbours, and how much filthy habits are injurious to them, as well as to ourselves if we unhappily adopt them, we surely need feel no hesitation in admitting the truth of the remark, that cleanliness is next to godliness.

Many of the precepts in the Mosaic Law are admirably calculated to promote individual and public health. There is one in particular, which enjoins the careful removal of offensive matter; the spirit of which might with advantage be religiously observed in the present day. Sir John Pringle, who most carefully studied the health of our armies, informs us, that, in two or three campaigns in which he was present, the want of care with respect to the camp privies was as destructive to our soldiers as the valour of the enemy. A few years ago, I was myself a witness to the prevalence of a severe dysenteric affection which prevailed amongst a number of Belgian brick-makers who were employed in the neighbourhood of Paris, and in whom the malady appeared, in great part at least, to depend on the extreme negligence with which they allowed excrementitious matters to accumulate, in hot weather, around the hovel which they inhabited. There is no one, who has taken any interest in the history of our nautical affairs, who can be ignorant of the vast improvement in the health of our sailors, and of the impunity with which they have made the longest voyages, since the importance of cleanliness and ventilation has been so well understood in our navy, and by the masters of private vessels. You are probably aware, that the

plague, in its most fearful forms, used formerly to visit, with almost exterminating severity, many cities in which it has long since been wholly unknown :— London affords one of the most striking examples which I could adduce. It is to the improved construction of these cities, and still more to the improved and more cleanly arrangements of their inhabitants, that this happy change is to be, in a great measure, attributed.

When we learn from modern travellers the present state of those places in which the plague is known still at times to prevail, we need feel no surprise that they do not participate in the exemption with which we are blessed. In some of these places, troops of wandering dogs are almost the only scavengers, to whom the filthy inhabitants supply abundant employment. In others, not only is drainage neglected, but the paths, being in part composed of wood, retain moisture, and add to the corrupting sources of disease.

Though our country has long been favoured to escape the plague, yet we are at times visited with prevailing fevers of greater or less severity. Now, it is notorious that these epidemics almost invariably break out in the closest and most filthy and crowded parts of our large cities and towns; such as, London, Edinburgh, Dublin, and Cork. To these parts they are often confined; and when they spread beyond these limits, it is still within them that they are the most severely felt. (2)

The arrangement of houses in narrow streets, confined courts, and closes without thoroughfares, tends very powerfully to make the different causes of disease existing in the air more certainly noxious.