Now, a number of careful investigations have been made of the constituents of miasmatic marshes in various parts of the world, with the following results: They contain from thirty to thirty-five per cent, of vegetable organic matter. This consists of humic, ulmic, cremic, and apocremic acids, all substances requiring renewed chemical investigation. Various minute vegetable algoid forms are revealed by microscopic examination—bacteria, vibriones, and microzymes. But all these so-called impurities are found in nearly every running stream and in many harmless well-waters, and to condemn water on account of their presence would be really to reject all waters, even rain, in which minute algoid vesicles (protococci) are often found. Even distilled water may contain bacteria and vibriones. Although, therefore, admitting that water may be contaminated by the presence of malaria, it by no means follows that this poisonous ingredient has any relation to the organic impurities mentioned, or that the latter are in any way injurious, but we should none the less be cautious as to the source of our drinking-water.
The stratum of air overlying typical malarial marshes has also been examined with particular care. It has been found to contain an excess of carbonic acid—watery vapor in large quantity—often carburetted hydrogen, and occasionally free hydrogen, ammonia, and phosphuretted hydrogen. If the marsh contains sulphates, sulphuretted hydrogen, is present. Its organic matter blackens sulphuric acid—gives a reddish color to nitrate of silver—has a flocculent appearance, a peculiar odor, and affords evidence of ammonia. The amount in Becchi's analysis was .000118 grain in each cubic foot of air. Ozone had no effect upon it. Besides this organic material, various vegetable and animal matters are arrested when the marsh-air is drawn through water or sulphuric acid—débris of plants, infusoria, insects, and even small Crustacea. Dr. Balestra has described spores and sporangia of a little algoid plant in the air of the Pontine Marshes. Lemaire and Gratiolet, in 1864, found in the air of one of the most unhealthy marshes of Sologne spherical, ovoid, and fusiform spores and a large number of pale cells, products, no doubt, of vegetable putrefaction. It has been supposed, by Schönbein and others, that ozone is deficient in marsh-air; that the quantity of ozone in the atmosphere and the prevalence of malarial diseases have an inverse proportion; and that ozone, by virtue of its supposed power of destroying organic matters in the air, is an antidote to miasm. There is, however, no evidence at all that ozone and malaria are antagonistic, or bear to each other any relation whatever. These various examinations, though interesting, bring us no nearer to a solution of the question, What is the nature of malaria? All of the many substances and forms thus far observed in malarial localities may be found equally in districts perfectly salubrious.
That it gains access to the system principally through the respira-
