It is useful for the traveller to bear diseases in mind from the standpoint of their etiology, as in this way he can more readily grasp the measures necessary for their prevention. Accordingly, the following classification is given, merely as a guide, together with a few examples. The diseases themselves, for the sake of convenience of reference, are grouped alphabetically and are not classified in any way. _Table of Diseases Classed according to Etiology._ A.—_Parasitic._ (i.) Due to “contact” either direct or through the agency of clothes, bedding, etc. Also due to direct inoculation through the skin or mucous membrane. _Examples_: Many skin diseases, venereal diseases, small-pox, tetanus, and blood-poisoning (septicæmia). (ii.) Due to “mouth to mouth” infection, through the agency of so-called “droplet” infection, expectoration, coughing, sneezing, etc. _Examples_: Influenza, pneumonia, and pneumonic plague. (iii.) Due to “droplet” infection, as above, or to infected scales from the skin, or to infected discharges from the nose, throat, or ear. _Examples_: Measles, scarlet fever, small-pox, chicken-pox, diphtheria. (iv.) Due to excremental infection through the agency of water, food, flies, fingers, dust, and soil. _Examples_: Enteric (typhoid) fever, dysentery, diarrhœa, cholera, worm infections of many kinds. (v.) Due to inoculation through the bites of insects, or the entry through skin abrasions of the infected excreta or infected crushed tissues of insects rubbed or scratched into these lesions. _Examples_: Malaria, yellow fever, tick fever, sleeping sickness, filariasis, relapsing fever, typhus fever, bubonic plague. (vi.) Due to invasion of the body by insects in their adult or larval stages. _Examples_: Chigger, myiasis of various kinds. B.—_Non-Parasitic._ (i.) Due to climatic conditions. _Examples_: Heat stroke, diarrhœa in some instances, constipation in many cases, rheumatism, prickly heat, chilblains. (ii.) Due to errors in diet. _Examples_: Diarrhœa, beri-beri, scurvy, sprue(?). (iii.) Due to poisons. _Examples_: Scorpion sting, snake-bite, vegetable poisons. (iv.) Miscellaneous. _Examples_: Bed-sores, epilepsy, apoplexy, concussion of the brain, hay fever, and other conditions into the cause of which a mechanical element frequently enters. It will be seen that some of these diseases, such as small-pox and diarrhœa, come under more than one heading, but this does not detract from the general utility of the above classification. _Bed-sore._ When a patient is confined to his bed for a long time it is necessary to support the lower part of the back on something soft, such as a pad of wool, or an extra pillow, in order to prevent the formation of a bed-sore; pillows should also be placed under the hips and heels. To harden the skin it is well to rub it with alcohol or to treat it with oil or white of an egg three parts, and spirits one part; zinc ointment is also useful for this purpose.