already stated, mosquitoes are known to be rare in certain spots where the conditions are naturally unfavourable to them all we have to do is to create similar unfavourable conditions by artificial means.

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Another popular error is that, even if we succeed in destroying all mosquitoes over a given area, they will swarm in again from the outside immediately after the measures are completed. But it should be clearly understood at once that all measures for the extermination of mosquitoes must be continued indefinitely, so that even if fresh insects do arrive from the outside they will not have an opportunity for multiplying within the given area. In other words, all towns which wish to be kept free from mosquitoes must determine upon, not a single effort, but a continuous one. In fact, just as all towns possess a staff of sweepers for the purpose of keeping its streets clean, so in the future must all towns in the tropics possess a staff of persons whose duty it will be to keep down these dangerous and troublesome pests.

3. General Principles to be Followed.-Suppose it were required to get rid of all mosquitoes from an island situated in mid-ocean. It would be possible to follow two courses. First, we might set about destroying every mosquito, either in the adult or in the larval stage. If this could be done with sufficient pertinacity, there can be no reasonable doubt that, in the end, the island would become entirely free of them-supposing, of course, that the insects cannot enter the island from without. Another method, equally promising, would consist in attacking not the insects individually but their breeding places; would consist in removing every drop of stagnant water in which

they breed, so that, ultimately, the insects would die out of themselves.

Now in our efforts to rid a locality which is not an island, we need follow only these same principles; but we must remember that, since in most non-insular places the insects can enter from without, efforts to destroy them individually will never be permanently successful. On the other hand, if we keep the area of operations entirely free of breeding places, we shall and must reduce greatly the number of insects, because, even if a few do manage to effect an entry from without, these will no longer be able to multiply within the area as they used to do. It is quite obvious, if we think of the matter for a moment, that one or two breeding places will give rise to fewer mosquitoes than 100 or 1,000 breeding places would do. If, for example, a given town contained 1,000 breeding places producing 100,000 mosquitoes daily, we are forced to conclude that the daily production of mosquitoes would be visibly reduced if all these breeding places were to be obliterated. Any mosquitoes effecting an entry from without would be so few in number, in comparison with the previous swarms of insects in the town, that they would scarcely be observed at all. If we consider the subject then in the light of these facts, we shall be able to decide upon the measure most likely to be profitable; and this is evidently that of removing all the breeding places. But concurrently it will do no harm to attack the insects individually whenever and wherever we meet them.

It has been a matter of serious difficulty to get people to understand these ideas, simple as they are. Even when the advisability of removing the breeding places has been

admitted, doubts as to the practicability of the measure have been entertained. Now the reader will remember that every new project is thought by many before it is tried to be impossible. After they have been tried, new projects often turn out to be not only possible but extremely easy. So it is with the present project. All we have to do is to keep a sufficient staff of men constantly employed upon the job.

Before showing how this can be done, we must describe the breeding places in greater detail.

4. The Breeding Places of Culex.-In the gardens and backyards of most houses, especially the houses of natives in the tropics, there are generally numerous tubs, pots, gourds, old buckets, broken flower-pots, empty oil tins and meat tins, broken bottles, and such like. During rainy weather, most of these contain a little rain-water; and wherever this water exceeds a few ounces in quantity, and has been standing long enough, there we shall find the larvæ of Culex. Tubs and cisterns employed for collecting rain-water from the roof, or for storing water for gardens, or even for keeping water for drinking, are favourite breeding places if they are left undisturbed long enough. Pots of water left by servants in the neighbourhood of cookrooms and in back verandahs, and then forgotten, are very suitable. We can even find larvæ in the tins of water placed under the feet of tables and meat safes for the purpose of excluding ants; or in gutters which carry rain from the roof, and which have sagged, so as to contain a little stagnant water after the rain has passed; or in uncorked empty bottles and sardine tins thrown on a dustheap; or in tin-lined packing cases; or in the hollows of

bamboos, drain-pipes, or even cannon-in fact, wherever a little rain-water can collect.

After the rains, Culex larvæ generally exist in collections of water made for gardening or household purposes; cisterns; gutters running from stables, cookrooms, and bathrooms; and old pits and wells. They may occur also in ditches, even in ditches which contain slowly running

water.

For practical purposes it is always most important to remember that when a large number of Culex exist in a given house, they are, in the large majority of cases, being bred just outside the windows. Thus we often find more Culex mosquitoes in one room than in another; and in such cases their larvæ can generally be discovered in a water-butt or flower-pot under the window of the infested room. A few insects may come from the backyards of our next-door neighbours, and still fewer from a little further away; but as a rule the Culex mosquito is a home-bred article. It is generally easy to prove this by destroying our own larvæ; after which a marked diminution of the winged insects in the house is almost certain to occur, even within twenty-four hours or so. And we must remember that it is these insects which carry yellow fever, elephantiasis, and perhaps other diseases, besides causing intense annoyance by night and day.

To those who really know about mosquitoes, it is always somewhat amusing to hear less well-instructed people complaining of the number of these pests which surround them, and which they often imagine are blown across seas and rivers by tornadoes, or are bred in countless myriads in neighbouring forests and marshes-the truth generally being that they are bred in their own backyards!

5. Breeding Places of Anopheles.-The habits of Anopheles, the malaria-bearing variety of mosquito, are somewhat different. These insects breed mostly, not in vessels of water, but in puddles on the ground. But they do not breed in all puddles, but only in those which suit them; and with a very little trouble it is possible to detect at sight the kind of water in which the larvæ will be found.

They are not often found in large bodies of water, such as lakes, where the surface is constantly ruffled by the wind, and where there are many fish to eat them; nor in large rivers; nor in rushing torrents; nor in well-contained ponds; nor in small but deep pools; nor indeed do they thrive much in the deeper parts of marshes and mangroveswamps. Nor, on the other hand, do they care for very small collections of water, such as the temporary puddles which form on the ground during a shower of rain; because in such puddles the larvæ perish almost at once as soon as the water dries up.

In my experience in India and Africa, Anopheles larvæ are found chiefly in small shallow puddles on the ground which are not so large as to contain minnows and waterbeetles, nor so small as to dry up too quickly. Such puddles are frequently found in depressions in the ground, in badly made drains and gutters, in places where water constantly oozes from the soil during the rains, or where the drainage is checked by out-cropping rock or by embankments and walls, or where water constantly escapes from pumps, stables, bathrooms, and irrigation channels. Small pools containing green mould or water-weed are much affected by the larvæ; and so are pools contained on the surface of weather-worn rock. But on the other hand,