664108-1887-Botanical-and-Afforestation-Department-Report-for-1886 — Page 15

SUPPLEMENT TO THE HONGKONG GOV" GAZETTE OF 30TH APR., 1887. 453

plain of Rajpoor, sixty or seventy per cent of the inhabitants are sometimes swept away by cholera in three or four days, while the wooded district of Sambalpoor is often free from it, or it is much less severe. The district commissioner, who had to make a tour in the district on account of the occurrence of cholera, reports among other things as follows:-

"The road to Sambalpoor runs for sixty or seventy miles through the forest, which round Petorah and Jenkfluss is very dense. Now it is a remarkable fact, but it is a fact, nevertheless, that on this route, traversed daily by hundreds of travellers, vehicles, and buggage-trains, the cholera rarely appears in this extent of sixty miles, and when it does appear it is in mild form; but when we come to the road from Arang, westward to Chicholes Bunglalon, which runs for about ninety miles through a barren, treeless plain, we find the cholera every year in its more severe form, the dead and dying lying by the wayside, and trains of vehicles half of whose conductors are dead.'

"In the same report Dr. BRYDEN continues :-

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"I will mention one other fact as a result of observations, namely, that places surrounded by those vast and splendid groves which are occasionally seen lying in low and probably marshy situations surrounded by hills, and which, from the mass of decaying vegetation, are very subject to fever in September, October, and November, are seldom visited by Cholera, and if it occurs there are but few deaths, while places on high groun 1, or in what are called fine, airy situations, free from trees and without hills near, so that they are thoroughly ventilated suffer very much from cholera.'

"MURRAY gives a number of instances showing the influence of trees on the spread of cholera, one of these may find a place here."

"The fact is generally believed and not long ago the medical officer of Jatisgar in central India, offered a striking proof of it. During the wile-spread epidemic of cholera in Allahabad, in 1859, those parts of the garrison whose barracks had the advantage of having trees near them enjoyed an indisputable exemption, and precisely in proportion to the thickness and nearness of the shelter. Thus the European Cavalry in the Wellington Barracks, which stand betwen four rows of mango trees, but are yet to a certain extent open, suffered much less than the Fourth European Regiment, whose quarters were on a hill exposed to the full force of the wind; while the Bengal Horse Artillery, who were in a thicket of mango trees, had not a single case of sickness; and the exemption cannot be regarded as accidental, as the next year the comparative immunity was precisely the same.'

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We need not however go to India to observe similar instances of the influence of a certain degree of moisture in the soil favoured by woods or other conditions; we can find them much nearer home. In the cholera epidemic of 1854, in Bavaria, it was generally observed that the places in the mors The great plain of the Danube' were saved, in spite of the otherwise bad condition of the inhabitants. from Newburg to Injolstadt was surrounded by places where it was epidemic, while in the plain itself there were but a few scattered cases. The same thing has been demonstrated by Reinhard, President of the Saxon. Medical College. Cholera has visited Saxony eight times since 1836, and every time it spared the northerly district between Plusse and Spree, where ague is endemie."

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'Even if these deductions must be accepted with caution fron an etliological point of view, stil!, on the whole, they indisputably tell in favour of trees and of wools.”

"Surface vegetation has also other advantages, besides its use in regulating the moisture in the soil; it purifies it from the drainage of human habitatious whereby it is contaminated and impregnate. If this refuse matter remains in soil destitute of growing vegetation, further decomposition sets in, and other processes are induced, not always of a salubrious nature, but often deleterious the products of A great deal of heat which reach us by means of air and water and may penetrate into our houses. is neutralized by evaporation from the leaves, anotlier portion by the decomposition of carbonic acid, just so much as is set free when we burn the wood and other organic combinations into the composition of which it enters. The heat produced by burning wood in a stove is derived from the sun; it is but the captured rays of the sun again set free by combustion. We learn from EBEMAYER'S work that the temperature of the trees in a forest, and even in the tops of them, is always lower than the air in the forest.'

"Besides this, shade in the open air always causes a certain draught which acts as a kind of fan. All must have noticed when walking in an oppressive heat, when the air seems still as death, that a refreshing breeze arises as soon as a clond casts a shade."

The air

"The shade of a single tree, therefore, cools not only by intercepting the sun's rays, but also by the effect of gentle fanning. The shelter of a thick wood, however, is much more agreeable than that of a single tree. The air in a wood is cooler than that of an open space exposed to the sun. from outside is drawn into the wood, is cooled by it, and cools us again. And it is not only the air that cools us, but the trees themselves. Observation has shown that the trunks of trees in a wood We therefore lose breast-high, even at the hottest time of day, are 5o Centigrade cooler than the air. considerable heat by radiation to these cooler objects, and can cool ourselves more easily at a tempe- rature of 25° Centigrade in a wood than at a much lower temperature in an open space.'

CHARLES FORd, Superintendent,

Botanical and Afforestation Department.

Printed and Published by NORONHA & Co., Printers to the longkong Government. Nos. 5, 7, and 9, Zetl:nd Street.