VENTILATION is the art of providing any confined area or apartment with an adequate supply of air in a condition suitable to the purposes for which it may be required. The air is usually introduced in a stream which maintains a freshness and purity of atmosphere in the place that is ventilated, any contaminated air being removed as the fresh air enters.
The progress of science has shown that no more prolific cause of disease and death exists among men than a vitiated and ill-regulated atmosphere in their habitations, whether it operate slowly and insidiously, producing scrofula, consumption, fevers, and other complaints; or, with sudden and extreme fatality, as in the Black Hole of Calcutta, in mines and wells loaded with carbonic acid, or in ships where the hatches have been battened down during storms. In a case that occurred a few years ago in the Irish Channel, every one below, about seventy altogether, was suffocated. Such examples, and the ever-active power of air during life, have at last established the conviction that much more attention ought to be given to this question than has usually been accorded to it, and that ventilation ought to be a primary instead of a secondary object in all architectural structures. It can never be so satisfactorily adjusted when it is merely introduced into buildings erected previously without any adequate provision for it. In numerous operations of nature and art, and more especially during combustion, respiration, and the decay that attends the putrefaction of animal and vegetable matter, unwholesome products are evolved; and so deleterious are these to animal life, that death is the necessary consequence when they accumulate in a concentrated form around the person. In a smaller proportion, they produce an endless variety of discomfort and disease, from a slight sense of languor or debility to the most violent apoplectic headache, suppressing for a time all attempts at exertion either of mind or body; while, on other occasions, they gradually undermine the constitution, and induce a permanent loss of health. In extreme cases death is indeed, more or less rapidly, according as the oxygen of the atmosphere is withdrawn, or an impregnation of poisonous gases communicated to it.
The air of respiration is the material agent that sustains and harmonizes all the physical changes in the human frame, supplying the important element that oxidizes the blood, consumes much waste animal matter, and contributes essentially to that organic chemistry
by which heat and electricity, as well as all special products, are developed in the living system. In the external atmosphere, air is constantly supplied to the bodies of animals, flowing to them on every side, and displacing the vitiated air which they produce. All habitations and other structures, or enclosed spaces for the use of man and other animals, must be provided with apertures for the ingress and egress of air, and additional means, when necessary, to secure the required supply. Without this they are deprived of the natural ventilation that is essential to life, and for which no other substitute can be given. We draw upon the atmosphere no less than 1200 times an hour, on an average, for nourishment and support, during the whole period of our existence; we consume oxygen and replace it by carbonic acid; and were air withdrawn from us, or changed much in its qualities, death would inevitably ensue. The air acts incessantly, not only on the blood as it passes through the lungs, but also on the surface of the body; and disease and death may arise from an unwholesome atmosphere in contact with the skin, even when the lungs are supplied with pure air. Well attested cases are recorded where severe oppression has attended the action of an amount of impurity so small as from th to th part of sulphureted hydrogen gas, while the absolute amount of impurity in air tainted by miasma is so excessively small, that its precise nature, as well as the minuteness of its weight in the most pestilential atmospheres, is unknown.
The supply of a fresh and wholesome atmosphere may accordingly be ranked among the first and most essential necessities of life. In the atmospheric ocean which rests on the surface of the terraqueous globe, a perpetual movement, or natural ventilation, is maintained on a great scale by numerous causes, more especially, however, by the unequal action of the rays of the sun on the equator and at the poles; the colder air moves along the surface from the poles to the equator, while the warmer air from the equator ascends and proceeds in a contrary direction towards the poles. These great and primary currents are modified in endless variety by the attraction of the sun and moon, the rotation of the earth, the relative effect of land and water, the ever-varying influence of local temperatures, volcanic action, meteorological phenomena, particularly the evaporation and deposition of moisture, the electrical condition of the air and of the surface of the earth, and the innumerable changes that attend chemical action in the mineral kingdom, as well as in those that occur in the organic world. The animal and vegetable kingdoms not only contribute to the movement of the air, but are the great causes of the most important changes induced in it, and the means of preserving the unity of its composition. The animal kingdom consumes its oxygen and produces carbonic acid, while, in the vegetable kingdom, the great tendency is to absorb carbonic acid and replace oxygen. But wherever these great movements are interrupted by local causes, or an undue accumulation of vegetable and animal debris takes place, there the right balance is not sustained; pestilential effluvia contaminate the air; and were it not for the wind, the rain, and the impetuous storms which, from time to time, visit such localities, and the operation of a peculiar diffusive power, in consequence of which no gas can accumulate permanently to the exclusion of other gases on the surface of the earth, whatever may be its specific gravity, they would at last become as fatal as the valley of death in Java, or the carbonic acid springs in Bavaria, in the grotto Del Lano in Italy, and other places notorious for their destructive atmospheres.
In selecting a site for a city, a house, or any establishment where numbers are crowded together, too much attention cannot be paid to its natural ventilation. An aspect towards the south, a dry gravelly soil, a moderate elevation securing efficient drainage and freedom of access to the air, with protections from offensive currents, and an immunity from local impurities, are great desiderata.
In the open air the temperature is generally under that of the body; and the air expired from the lungs, and also that in contact with the surface of the body, being expanded by the heat which it receives, escapes from its levity, and a fresh stream is immediately supplied; but when the body is confined within a limited space, special arrangements must be made to admit of a constant renewal of fresh air.
This ventilation must be modified and adapted to the circumstances of each individual case, and the state of the external air. It is a subject, therefore, of great extent, and as various in its details as the climate in which we live, the habitations in which we dwell, the occupations in which we are engaged, the food on which we live, the means of protection against heat and cold, and the peculiarity of constitutions which each may have. We shall therefore content ourselves in the space allotted to this article, by pointing out the leading facts connected with the more prominent objects which it includes in reference to the frame of man. It must not, however, be forgotten that this branch of science is as yet so imperfectly attended to, that it is impossible to turn to any city
without seeing much discomfort, disease, and even death, induced from time to time by ignorance of the laws of ventilation; and, in assemblies of every variety, the whole audience is not only too frequently subjected to extreme uneasiness, but the tone of the mental faculties, and the capacity for exertion and attention, are also affected by the state of the atmosphere.