The _Anopheles_ mosquito, which is the one that transmits malaria, often exists in localities where the more common varieties do not occur, and on account of the habits of this insect their presence is liable to be overlooked. They seldom attempt to bite during the day, and it is only rarely the case that they try to do so at night in a well lighted room;--particularly where movement of any kind is going on. During the day this mosquito remains perfectly quiet in the dark corners of the house, and is very fond of resting on cobwebs, presenting, when doing so, an appearance strikingly similar to that of fragments of leaves, soot or of other natural objects that are frequently found suspended on such structures. On account of these peculiarities and for the further reason that the insect bites mainly just following daybreak, when the victim is profoundly unconscious in sleep, its presence often remains undetected, and as a consequence we occasionally hear from those who do not take the trouble to inform themselves that malaria exists in this or that locality where mosquitoes do not occur. The yellow-fever mosquito bites for the most part during the day, but will do so at any time when there is light. In districts where this disease occurs it is quite as important to prevent its entrance as that of the malarial mosquito. Not only does screening prevent malaria and yellow fever, but it keeps out flies and other insects that unquestionably bring with them the germs of other diseases. There now remains no doubt that several affections, notably typhoid fever and dysentery, are frequently communicated by means of the common house-fly, which spends its time alternately on the fecal material around privies or in other filth, and in our kitchens and dining-rooms; it is one of the most astounding evidences of the power of habit, in the face of common sense and ordinary decency, that we have not long ago taken active steps to rid ourselves of its disgusting presence. Fortunately in screens we have a perfect barrier to the entrance of flies, and no house can be considered complete without being thoroughly equipped with these all-necessary appliances. It is scarcely possible to overestimate the economy that results from the use of screens; among the various means employed for conserving the public health they take first rank, and undoubtedly insure those who live in houses to which they have been added an immunity against the costly effects of disease that could scarcely be computed. A house would be more habitable without chairs, beds, or tables than screens, since in the absence of the former we may be healthy, though somewhat uncomfortable, but without the latter serious disorders are pretty certain, sooner or later, to make their appearance.