It must be remembered, however, that it has been long a matter of popular belief in the Campagna that malaria was, in some way, caused by mosquitoes; and it is the difficulty of convincing those in high authority of this fundamental fact that is at the root of the indifference and inertia which oppose all attempts at amelioration in India and in many of our colonies. During the first two years’ experiments on the Campagna, out of 25 protected cottages, with a population of 173 persons, only 8 persons contracted malarial fever; while in 30 unprotected cottages, having a population of 220, only 17 escaped the disease; although the protected and unprotected cottages were, as far as possible, paired as regards the site, and were otherwise of a uniform plan of construction, and all inhabited by the same class of railway subordinates. The system is the one above all others most suited for adoption by private persons, because it secures an almost complete immunity in spite of the most unfavourable surroundings, and renders the user quite independent of the sanitary lapses of his neighbours; but in spite of this, the plan is almost ignored in our English colonies and dependencies, though the writer has recently received an interesting communication from a medical man practising in China who has adopted it with signal success. Professor Celli’s plan consists in rendering habitations impervious to the entry of insects by closing all openings with wire gauze (mesh of about 12 strands to the inch). All windows, as well as such doors as only serve as such, and are not absolutely required for ingress and exit, are permanently closed by frames covered with the gauze, and all indispensable exterior doors are fitted with _double_ spring doors of the same material, sufficiently separated from each other to secure the closure of the first door before the second can be opened. In most Tropical residences, the number of doors is far in excess of actual needs, it being nothing uncommon to find rooms with four or five doors, all opening in the exterior. Though desirable and even necessary for free ventilation, no room can possibly require more than a single door opening on the outside, and in a well-planned house with suitable corridors, there is no real necessity for more than one or two exterior doors to the whole house. All outside doors, then, not absolutely necessary as such, should be treated as windows and permanently closed with single frames of wire gauze, so that the number of the more expensive double spring doors may be reduced to a minimum. In Tropical climates it is, however, essential that a considerable area of verandah should be included within the protected area, as a good deal of time is necessarily most pleasantly spent in the verandah, not only in the evening, but during the rains throughout the whole day. On this account a northern verandah should be the one selected for protection in this way.