A manual of practical hygiene / by the late Edmund A. Parkes.

  • Edmund Alexander Parkes
Date:
1891
Catalogue details

Licence: Public Domain Mark

Credit: A manual of practical hygiene / by the late Edmund A. Parkes. Source: Wellcome Collection.

    37/844 (page 13)
    evaporation equalled 212 inches, while the rainfall was only 25'6 inches; this shows how much water was abstracted from the soil, and how the air must have been moistened and cooled. Observations in Algeria (Gimbert) have shown that Eucalyptus globulus absorbs and evaporates 11 times the rainfall; extremely malarious places being rendered healthy in this way in four or five years. The hottest and driest places in the tropics are those divested of trees.^ Vegetation produces also a great effect on the movement of air. Its velocity is checked; and sometimes in thick clusters of trees or underwood the air is almost stagnant. If moist and decaying vegetation be a coincident condition of such stagnation, the most fatal forms of malarious disease are produced. It may thus do harm by obstructing the movement of air; on the other hand, it may guard from the currents of impure air. The pro- tective influence of a belt of trees against malaria is most striking. In a hygienic point of view, vegetation must he divided into herbage, brushwood, and trees ; and these should be severally commented on in reports. Herbage is always healthy. In the tropics it cools the ground, both by obstructing the sun’s rays and by aiding evaporation; and nothing is more desirable than to cover, if it be possible, the hot sandy plains of the tropics with close-cut grass. Brushwood is frequently bad, and should often he removed. There is, however, evidence that the removal of brushwood from a marsh has increased the evolution of malaria, and that, like trees, brushwood may sometimes offer obstruction to the passage of malaria. It must also he remembered that its removal will sometimes, on account of the disturbance of the ground, increase malarious disease for the time; and therefore, in the case of a temporary camp in a hot malarious country, it is often desirable to avoid disturbing it. When removed, the work should be carried on in the heat of the day, ^.6., not in the early morning or in the evening. Mr W. ISTorth instances the case of Cisterna, where the removal of macchia (^.e., brushwood, &c.), though long objected to on account of supposed protection from malarial currents, was the means of improving the healthiness of the district.^ Trees should be removed with judgment. In cold countries they shelter from cold winds; in hot they cool the ground; in both they may protect from malarious currents. A decided and pernicious interference with the movement of air should be almost the only reason for removing them. In some of the hottest countries of the world, as in Southern Burmah, the in- habitants place their houses under the trees with the best effects; and it was a rule with the Homans to encamp their men under trees in all hot countries. The kind of vegetation, except as being indicative of a damp or dry soil, does not appear to he of importance. 3. Absorption of Heat.—The heat of the sun is absorbed in different amounts by different soils equally shielded or unshielded by vegetation. The colour of the soil and its aggregation seem chiefly to determine it. The dark, loose, incoherent sands are the hottest; even in temperate climates 1 It has been proposed (by Mr Milne Home) to plant trees in Malta, with the view of improving and regulating the water-supply. Mr Robert L. Stevenson has considered the thermal influence of forests, in a paper in the Proceedings of the Royal Society of Edinburgh (19th May 1873). 2 B.M.,1 y April and May, 1887.