room is fairly indicated by the following statistics, the result of a large number of observations made by Mr. Richard Weaver in the schools and manufactories of Leicester, England: As carbonic-acid gas is usually the chief impurity in rebreathed air, being produced in large quantities by both breathing and combustion, Mr. Weaver takes it as the measure of aerial contamination, the amount present under ordinary circumstances enabling us to judge of the degree of vitiation caused by the other products of respiration and combustion. Setting out with the established fact that free or what is commonly called pure air contains, for every thousand parts, very nearly four-tenths of one part of carbonic acid, Mr. Weaver found in the air of a room where six persons worked at boot and shoe finishing, each person having 51 cubic feet of space, that the proportion of carbonic acid was 5.28 parts per thousand, or more than thirteen times as much as Nature, when let alone, allows. In another instance, where the air-space to each of fourteen individuals was 186 cubic feet, with fourteen gas-lights burning, the amount of carbonic acid, to a thousand parts of air, was 5.32. In a class-room of one of the national schools, and the science class-room at that, seventeen pupils, each with 200 cubic feet of space, were breathing an atmosphere containing 2.41 parts per thousand of carbonic acid, or six times as much as the air contains in exposed situations. In no case examined was the proportion of carbonic acid as low as one part in a thousand of air; the average in fifteen places being 3.14 per thousand, or nearly eight times as much as in pure air. It is hardly necessary to add that the provisions for ventilation, where any thing of the kind was attempted, were of the most imperfect character. But what may be effected by ventilation was strikingly shown in the instance of a boy's day-room in one of the national schools, where there were one hundred pupils, each with 236 cubic feet of air-space. The ventilators were placed in the roof, and, though very far from perfect, the air in the room contained only 1.16 parts of carbonic acid to the thousand, the lowest proportion observed in any of the fifteen cases examined. Mr. Weaver states that the atmosphere in several of the rooms was very offensive, and in every case a pleasurable sense of relief was experienced on entering the outer air. Large space, without ventilation, he considers of little avail, as it has no advantage over a small room except that the air is a little longer in attaining the same degree of contamination.
Careless Disinfection.—In cleansing and disinfecting rooms that have been occupied by persons sick with contagious diseases, mere exposure to disenfecting vapors is not enough to thoroughly rid the apartment of danger to future inmates. The floors and wood-work require thorough scouring with some disinfecting fluid, and the walls and ceiling should also be carefully cleaned. If the walls are covered with paper, nothing short of its removal will be effectual, as it unquestionably has the power of absorbing and retaining contagious matters, that are not reached by the ordinary processes of disinfection. And its removal is all the more necessary where several thicknesses are plastered on the wall, for then the deeper layers are quite beyond any possibility of being cleansed; and, apart from the danger of contagion, the presence of paste in such quantities, as several thicknesses of paper involve, liable in warm weather to ferment and decompose, and at all times furnishing a nest for hosts of vermin, is certainly most objectionable. That wallpaper does actually furnish lodgment for contagion, and the paste with which it is stuck on food for vermin, is proved by the following cases reported in the Lancet: The workmen engaged in stripping the paper from the walls of a house in Manchester, that had previously been occupied by persons ill with fever, nearly all came down with the same fever, although previous to their visit the house had been disinfected with chlorine and carbolic acid. In the Knightsbridge barracks, where numerous layers of paper and paste had been allowed to accumulate, the walls when examined were found to be literally swarming with maggots, that were leading a most flourishing existence while subsisting on the paste between the several thicknesses of paper. The practice of freshening the walls of rooms by covering up, instead of removing the filth, has become ex-
