Between the north-eastern borders of the Transvaal and the coast lies the Portuguese colony Mozambique. Its frontier railway station, Ressario Garcia, is near that of the Transvaal, viz., Komati poort, which is 53 miles from Delagoa Bay. A low-lying country extends from the coast about 100 to 200 miles inland, and is tropical. Except some elevated spots, the whole of it is almost uninhabitable in summer by whites on account of malaria. During some specially bad seasons natives even succumb to that malady. The only comparatively safe months are from June to November. Marshy localities, and wherever there is shaded rank vegetation in low-lying parts, are dangerous all the year round; in such places the water is deadly at all times unless first boiled.

This malarial poison is distinct from that which produces yellow fever in America, and is so far unlike it as it is not contagious. The theory is that the poison is produced below the surface by decaying vegetable matter in low and dank parts during the more inactive but still warm and sunny winter season and during the hot months preceding the summer rainfall. Upon the first rains the malarial poison escapes through the then softened crust in the shape of vapoury miasms. This happens during the night, after the surface of the earth has been cooled off. Those miasms are dissipated or neutralised by the action of the sun. The dewy grass retains the poison until it is thoroughly dried to the root. All surface water is liable to that poisonous impregnation. Malarial manifestations occur all over South Africa, but in progressive degrees of virulence with the advance to warmer latitudes, and with the descent from the high table-lands to the coast levels. On the Transvaal high veldt, for example, a mild form is developed which, in midsummer, to a small extent, affects and kills sheep. It is called blaauwtong, and does not affect horses. Descending further, this danger to sheep increases and begins earlier. Below 5,000 feet altitude in the Transvaal the summer season is dangerous to sheep, and horses and mules are subject to horse sickness; whilst lower still the same malaria attains sufficient virulence to attack human beings, and becomes very deadly upon levels nearing the coast. Komati poort, the frontier railway station already mentioned, is dreaded as a still worse death-trap than even Delagoa Bay, where it is very unsafe, say, from December to end of April. The season of horse sickness terminates upon the appearance of the first sharp frost in May. The safeguards for human beings consist in avoidance at night and early morning of low-lying localities, or such elevated places even which are subject to be invaded by miasmatic emanations produced on and wafted from dangerous lower levels. Drink no unboiled water except that from deep wells or rain-water; maintain careful and moderate diet, active habits, but avoiding extreme exertions and excitements; a very sparing use of alcoholic drinks, preferably taken with the regular meals, is admissible.

Donkeys, horned cattle, and goats are exempt from malarial risks.

For horses and mules no certain remedy appears as yet to be known. The best research, on behalf of the Transvaal Government, by specially requisitioned French bacteriologists, assisted by that famous microbe-hunter, Dr. Theiler (Dr. Theiler is the Transvaal veterinary surgeon and chief of the Medical Laboratory, Pretoria, a noted Swiss savant, who, with the aid of the said French experts, discovered the rinderpest inoculation remedy), has failed to find the bacillus of horse sickness. Barely five per cent, of the horses attacked recover, and about ten per cent, of mules. These are then called salted, and are immune from horse sickness; they can after that be safely used in the worst localities, and are correspondingly more valuable. They are, however, liable periodically to light after-attacks, when it is safer to exempt them from work for a day, or for a few hours at least.

Some proprietors of mail coaches are in the habit of administering doses of arsenic to their horses and mules, which are said to operate in lessening the death rate and to favour the salting process.

As safeguards for horses and mules, the following rules have been found to minimise losses in dangerous tracts where the low clinging miasmatic vapours are so deadly during the night and earlier parts of the morning. (During rainfall there is hardly any danger, nor is there after a night's rain for the day following):—

Do not traverse low suspicious tracts during the hours between 9 p.m. and, say, two hours after sunrise, lest poisonous vapours be encountered and inhaled by man or horse.

Choose the most elevated spots for camping out at night. No grazing to be allowed from 10 p.m. to about 10 or 11 a.m., unless it is raining. Dewy grass is fatally poisoned; the heavy moist air close to the surface is also suspected. Grazing is only safe after the soil and grass are dried of all dewy moisture.

Avoid all water of at all a stagnant nature; rather let the animals remain thirsty.

If the animals have been fed with dry fodder during the night, let the first morning stage be moderate and not exhausting. With empty stomachs the task might be somewhat increased, but even then it should be less than any other succeeding stage. When the first symptoms of sickness are noticed they may pass over if the animal is at once freed from work and allowed to rest, or is at most led when marching. Among the most dangerous places for horse sickness and for fever to human beings are the luxurious dongas, ravines, and valleys which abound along the long stretches of mountains and broken country immediately below the high plateaux.

The passes leading up to the high veldt are few in number, and so precipitous as to be almost impracticable for vehicles. Of late years those roads have been allowed to fall into disrepair, in order, it may be supposed, to check wagon traffic and to promote that by railway; apart from the railway, communication with Delagoa Bay would now be impossible. What with the fever climate in summer, and the formidable mountain barriers, the Transvaal high veldt is well protected from aggression from the direction of Delagoa Bay. A few thousand men distributed at the few mountain passes, blocking the tunnel at one of these (at Waterval Boven), and breaking up some few bridges, would effectually arrest the progress of any invading force.