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toms of influenza and the symptoms of an over-dose of ozone. Experiments on animals have shown that irritation of the mucous lining of the throat and nostrils, with febrile symptoms and congestion of the lungs, may be quickly excited by breathing air containing a large percentage of ozone. If animals are, for a long time, subjected to ozone, they perish. In their susceptibility to it, however, they vary widely. A rabbit, breathing air mingled with 1⁄2000 of its weight in ozone, has died in two hours. Mice, breathing air about 1⁄6000 of ozone, have died immediately. Rats are more susceptible than Guinea pigs, and Guinea-pigs are more susceptible than rabbits. Pigeons are quite tolerant of ozone, and frogs are proof against it, provided they have abundance of water. Birds are specially tolerant of this agent, as might naturally be inferred, since, in the higher strata of the air, where they fly, ozone is more abundant than near the earth.

It has been stated that there is a relation between ozone and intermittent and remittent fevers; that rheumatism is prevalent when ozone is deficient; that, when ozone is in excess, diphtheria, quinsy, small-pox, herpes, measles, scarlatina, and other cutaneous affections, prevail; and that, during the visitation of the cattle-plague in England, ozone was below the usual standard.

There is considerable more of evidence to show that visitations of cholera are accompanied with a diminution in the atmospheric ozone.

Experiments have shown that germs, sporules, bacteria, vibriones, and small monads, with other low forms of life, are destroyed by ozone. On the accepted view that epidemic and infectious diseases are caused by spores, bacteria, etc., we can understand how a deficiency of ozone in the air may invite disease.

The only conclusions on this subject of the relation of atmospheric ozone to disease, that at present seem justifiable, are these:

1. A deficiency of ozone in the air probably has a certain relation to epidemic and chronic disease.

2. Deficiency of ozone invites disease, by debilitating the system, and thus making it less capable of contending with morbid influences.

Tests for Ozone.—Of the various tests for ozone, those which are most used are starch and iodide of potassium. Fox prefers the iodized litmus and the simple iodide of potassium test. The litmus-paper and the iodide of potassium must both be pure. The Swedish filtering-paper is the best. Blue litmus is purified by boiling, etc., until it is of a vinous red color. The strips of filter-paper are plunged for one-third of their length into a solution of neutral iodide of potassium, made by dissolving 151⁄2 grains in 321 grains of distilled water.

These tests are exposed to the air for twelve or twenty-four hours beneath a plate. If ozone be present in the air, the iodized part becomes blue, and the non-iodized part is unchanged. Sometimes the test-paper is placed in ozone-boxes, so constructed that a current of air passes through them.