Further, strong suspicion, approaching moral certainty, strongly points to certain flies, of the class known as horse and cattle flies, as the species that acts as the intermediary. These flies are much more common in tropical climates than they are at home, and are characterised by the peculiar persistency with which they attack an animal, in spite of all attempts to drive them off; and so much is this the case that nothing short of pursuing the insect until it is killed is of any use. They do not, as a rule, invade houses, and it is exceptional for them to attack man, but they will do so occasionally, and the stab they give is so sharp that it is hardly likely to be overlooked. At present the disease appears confined to Africa, but species of the same flies are to be found in India, and the writer has more than once been bitten by them, though no danger attaches to the incident, as the specific germs of the disease do not occur in that country. [Illustration: FIG. 14.--Drawing of the fly concerned in the Tsetse, or Trypanosome, disease of horses.] They are usually dark grey, flattened insects, with a peculiarly hard integument, which forms so efficient a protection against injury that, if merely squeezed between the fingers, they will commonly fly away in a perfectly unconcerned manner. The easiest way to dispose of them is to knock the insect down with the whisp of horsehair mounted on a cane, commonly carried by horsemen when flies are troublesome, and then to crush it under the boot, giving the foot a good twist, so the wound, like that of the sergeant-instructor’s bayonet, may be “made incurable.” The general appearance of these insects may be best gathered from the above magnified figure. It is obvious that as far as our knowledge extends, the prevention of sleeping sickness is purely a matter of avoiding being bitten by insects of this sort, and it is also clear that as far as indoor life is concerned, the adoption of metallic gauze protection of the house will be as effectual as it is in the case of malaria. These flies are, however, mainly forest insects, and watchfulness, especially when sitting out of doors, is all that can be suggested. Personally, if bitten by one of these flies in a country where sleeping sickness exists, I should be strongly inclined to destroy the bit of tissue around the bite by means of some powerful caustic, such as pure carbolic acid dropped into a small cut at the site of the puncture, for as yet no instance of recovery from the disease has ever been met with, and in all probability this measure, if done with tolerable promptitude, would probably suffice to destroy the germs before they gained access to the general circulation. SUNSTROKE AND HEAT APOPLEXY. The disturbances of the nervous system that are grouped under the above heads vary a good deal, and probably comprise several different diseases, with as many distinct causations.