, Mr. Dancer, F.R.A.S., has been examining the dust of our cities. The results are not pleasing. We had always recognised city dust as a nuisance, and had supposed that it derived the peculiar grittiness and flintiness of its structure from the constant macadamizing of city roads. But it now appears that the effects produced by dust, when, as is usual, it finds its way to our eyes, our nostrils, and our throats, are as nothing compared with the mischief it is calculated to produce in a more subtle manner. In every specimen examined by Mr. Dancer animal life was abundant. But the amount of ‘molecular activity’—such is the euphuism under which what is exceedingly disagreeable to contemplate is spoken about—is variable according to the height at which the dust is collected. And of all heights which these molecular wretches could select for the display of their activity, the height of five feet is that which has been found to be the favourite. Just at the average height of the foot-passenger’s mouth these moving organisms are always waiting to be devoured and to make us ill. And this is not all.

As if animal abominations were insufficient, a large proportion of vegetable matter also disports itself in the light dust of our streets. The observations show that in thoroughfares where there are many animals engaged in the traffic, the greater part of the vegetable matter thus floating about266 ‘consists of what has passed through the stomachs of animals,’ or has suffered decomposition in some way or other. This unpleasing matter, like the ‘molecular activity,’ floats about at a height of five feet, or thereabouts.

After this, one begins to recognise the manner in which some diseases propagate themselves. What had been mysterious in the history of plagues and pestilences seems to receive at least a partial solution. Take cholera, for example. It has been shown by the clearest and most positive evidence that this disease is not propagated in any way save one—that is, by the actual swallowing of the cholera poison. In Professor Thudichum’s masterly paper on the subject in the ‘Monthly Microscopical Journal,’ it is stated that doctors have inhaled a full breathing from a person in the last stage of this terrible malady without any evil effects. Yet the minutest atom of the cholera poison received into the stomach will cause an attack of cholera　Two considerations must have caused Scheer the gravest possible anxiety.. A small quantity of this matter drying on the floor of the patient’s room, and afterwards caused to float about in the form of dust, would suffice to prostrate a houseful of people.

We can understand, then, how matter might be flung into the streets, and, after drying, its dust be wafted through a whole district, causing the death of hundreds. One of the lessons to be learned from these interesting researches of Mr. Dancer is clearly this, that the watering-cart should be regarded as one of the most important of our hygienic institutions. Supplemented by careful scavengering, it267 might be effective in dispossessing many a terrible malady which now holds sway from time to time over our towns.