favours the growth and circulation of micro-organisms, producing disease.
The dust in the air contains, among other things, bacteria, innumerable epithelial scales from the skin of men and animals, hairs, fragments of wool, cotton and flax fibres, pollen grains, splinters of wood, bark, shreds of leaves, particles of coal and many other substances. Some of these irritate the lungs mechanically, as, for example, anthracite or bituminous coal, which gives rise to miner's consumption; the fine particles of steel thrown off in grinding saws and other instruments; the dust in potteries, and the fragments of wool flax, etc., in cloth factories and cotton mills: all exert an injurious influence upon the lungs.
The great remedy for the impurity of the air within doors is ventilation; and the best method of accomplishing this has been for many years one of the great problems of science.
As the air of an inhabited room cannot, at the best, be as pure as the external atmosphere, the problem of ventilation is to reduce the impurities of respiration to the point where health will not manifestly suffer by drawing them into our lungs again.
In order to keep the ratio of carbonic acid and its associated animal impurities down to this limit, it has been found by experiments that it is necessary to supply 3,000 cubic feet of perfectly pure air each hour for every adult person who is vitiating the atmosphere of a room by his breath.
It must be remembered also that the gas-lights and other sources of illumination (the electric lights excepted) exercise a powerful influence in rendering the air of an apartment impure, by exhausting the oxygen, and giving off various products in combustion.
With natural ventilation, that is, ventilation from the cracks of doors and windows, and open fireplaces, it is almost impossible to replace the air of a room more than three times in an hour without the inmates being exposed to unpleasant currents of air. To observe the best hygienic conditions, therefore, it would be necessary that persons should not congregate in a room to a greater number than one to every 1,000 cubic feet.
An apartment 10 feet high, 10 feet wide, and 20 feet long, should thus contain 2 persons; and in a room 20 feet square and 10 feet high 4 persons, but no more, would be able to sit, eat, or sleep. But as it is impossible always to regulate the number of occupants thus, the simpler and entirely feasible plan of always having one window in each room opened at the top, should be invariably observed.
Of course all such laws of health are constantly outraged, but sooner or later such violations are sure to entail their own punishment.
Pure Water.—Water is the second great material necessary for existence. Without food or water life has been prolonged for 14 days. Without food, but with access to water, a man has lived for over 8 weeks.