Volume 3

A system of medicine / by many writers ; edited by Thomas Clifford Allbutt and Humphry Davy Rolleston.

Date:
1905
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: A system of medicine / by many writers ; edited by Thomas Clifford Allbutt and Humphry Davy Rolleston. Source: Wellcome Collection.

Provider: This material has been provided by King’s College London. The original may be consulted at King’s College London.

    27/1099 (page 3)
    j proportion of wluit ;ire regai'ded as tropical diseases—the limitations of certain diseases to warm climates are in no sense dependent on the action of temperature on the human body, or on food, or on social and sanitary (•onditions. Nor with few exc'eiitions do they depei'id on the action of the atmospheric temperature on the disease-germ itself while the germ is located in the human body. They depend directly or indirectly on the requirements of the germ when it has escaped fi-om the human body, and during its jtassage from human host to human host. During this passage the germs of tropical diseases demand tropical conditions; hence the geographical or rather climatic limitations of these diseases. So tar as we know them, the vast majority and all the important disease-germs of man belong to one or other of the following classes ; Bacteria, Fungi, Protozoa, Helminths. Bacteria.—\’ery few of the diseases special to the tropics oi' warm climates are bacterial, and it is difficult to explain how it is that these few even—Malta fever for example—should be so limited. For a bacterium is not injuriously affected by ordinary atmo.spheric conditions, and shonld be able to p-ass from man to man, whether directly, or in- directly from a saprophytic condition, in any climate. Accordingly the vast majority of the bacterial diseases of man are of Avide distribution. On the other hand the A-ast majority of diseases having climatic limitations—tropical diseases among them—are caused by {a) Fungi, {}>) Protozoa, (c) Helminths,—organisms Avhich, as a rule, one AA'ay or another, require in their passage from host to host very special and often complicated conditions. {a) Fungi.—Fungi living on the surface of the body are just as exposed to climate as are ordinary j)lants. Some of them demand a hot and moist climate, hence they are found oidy Avithin the tropics and in particular parts of the tropics. Tinea imbricata, pinta, and pi'obably other and as yet undctei-mined epiphytic diseases belong to this category. ^\Tlen Ave speak of a disease as being a ti'opical disease, avc mean merely that the disease-germ can be acf[uired only iti tiopical conditions. Once the germ is acquired the di.sease I'uns its course in any climate. The only exception to this general statemcmt lies in the epiphytic di.seases. In those of them special to the tropics the germ itself, even after im- plantation and thorough establishment, still i-ecpiires tropical conditions ; on the patient (putting those conditions the germ dies and the disease it gave ri.se to disappears. In a semse, thei'cfore, these e})iphytic diseases are the ordy ti'ue tropical diseases. (b) Protozoa.—The jjathogenetic protozoa are responsible [)robabl} for a A'ery large number of diseases. Many appear to l)e aide to pass directly from host to host, unaffected apparently by the atmospheric conditions they encounter on the passage; that of small-po.x and of most of the exanthematous fevers probably beloTig to this category. Others, on the contraiy, demand special climatic conditions. 8uch are the gcian of scarlet fever Avhich does not spread in the tro])ics, and the germ of dengue Avhich, conversely, docs not spread in cold climates. That of the