Although in no sense a malady in any way peculiar to hot countries, Europeans are necessarily much more exposed to infection among semi-civilised communities, where vaccination is at best only partial, than in Europe; and hence it is well to impress the necessity of efficient re-vaccination on all who have to live among people by whom the blessings of vaccination are, as yet, imperfectly appreciated. Even a single vaccination affords so great a protection that it is rare to meet with fatal cases amongst those who are foolish enough to live in the midst of small-pox without being re-vaccinated, but it is hardly worth while to risk suffering from so revolting a disease, with the chances of disfigurement for life, for the sake of avoiding so trifling an inconvenience as that involved in the little operation. On this account it is very desirable for the intending emigrant to tropical parts to be re-vaccinated before starting, as an inflamed arm is much more troublesome when complicated with prickly heat than it is in temperate climates. In addition to this, it is always wise to submit to re-vaccination whenever an epidemic of small-pox is raging around one. If needless, the virus will not “take,” and you will suffer nothing worse than the trifling scratch involved in the operation. If, on the other hand, it “takes,” it shows that a grave risk would have been run in neglecting the precaution. SLEEPING SICKNESS. This peculiar malady has only come into notice of late years, since the opening up of Central Africa, and though it was at first thought to be confined to the negro race, has recently been shown to occasionally attack Europeans. In its early stages, the disease presents many points of resemblance to ordinary malarial fever, and has usually been confused with it, both by patient and doctor; but following this, after an interval of a few weeks or months, certain peculiar nervous symptoms appear, from which the disease has taken its name, and which are mainly characterised by hebetude and somnolence. It would be superfluous, in a work like the present, to enter into any details as to its peculiarities, especially as our knowledge on the subject is at present in its infancy. It may, however, be fairly said that we are almost certain that the disease is caused by certain peculiar parasites (_Trypanosomes_) that are found in the early feverish stage of the disease in the blood, and subsequently, when the peculiar sleepiness appears, in the fluid that bathes the spinal canal. From the analogy of malaria, as well as from anatomical considerations, it is tolerably certain that the disease is conveyed from one human being to another by means of inoculation through the agency of biting insects.