_The Relation of Soil generally to certain Bacterial Diseases._ Recent investigations have, in effect, considerably added to our knowledge of pathogenic germs in soil; and whilst the three species enumerated above are still considered as types normally present in soil, it must not be forgotten that other virulent disease producers either live in the soil or are greatly influenced by its conditions.
Fränkel and Pasteur have both demonstrated the possible presence of anthrax. Fränkel maintained that it could not live there long, and at ten feet below the surface no growth occurred. This may have been due to the low temperature of such a depth. Pasteur held that earthworms are responsible for conveying the spores of anthrax from buried carcasses to the surface, and thus bringing about reinfection. Cholera, too, has been successfully grown in soil, except during winter. The presence of common saprophytes in the soil is prejudicial to the development of the cholera spirillum, and under ordinary circumstances it succumbs in the struggle for existence. From experiments recently conducted for the Local Government Board by Dr. Sidney Martin, evidence is forthcoming in support of the view that the bacillus of typhoid can live in certain soils. Samples of soil polluted with organic matter formed a favourable environment for living bacilli of typhoid for 456 days, whereas in sterilised soil, without organic matter, these organisms lived only twenty-three days. Tubercle also has been kept alive for several weeks in soil.
In passing, a single remark may be made in relation to the long periods during which bacteria can retain vitality in soil. Farm soils have, as is well known, been contaminated with anthrax in the late summer or autumn, and have retained the infectious virus till the following spring, and it has even then cropped up again in the hay of the next season. In 1881 Miquel took some samples of soil at a depth of ten inches, containing six and a half million bacteria per gram. After drying for two days at 30° C., the dust was placed in hermetically sealed tubes, which were put aside in a dark corner of the laboratory for sixteen years. Upon re-examination it is reported that more than three million germs per gram were still found, amongst them the specific bacillus of tetanus. Whether or not there is any fallacy in these actual figures, there is abundant evidence in support of the fact that bacteria, non-pathogenic and pathogenic, can and do retain their vitality, and sometimes even their virulence, for almost incredibly long periods of time.