An oft-repeated statement is ‘Man is a tropical animal’ but, one would suggest, the tense of the verb is wrong and should be ‘was’, especially in the case of the European dweller who is heading for the tropics for the first time.
The body possesses the mechanism necessary to survive in hostile, hot climates, but time is required to evoke them. The adaptive process takes one, two or three weeks depending on the severity of the hot climate. Briefly, the strain on the body is shown by a high pulse rate and body temperature, and the condition will progress to one or other of the heat illnesses (see below) unless the stress is lessened or muscular activity reduced.
With graded exposure and gently increasing activity, the sweat glands are trained to produce more, start more quickly, continue longer without sweat-gland fatigue and to retain more salt in the body. The circulatory system (heart and arteries) learns to absorb water in much larger quantities from the stomach and intestines and to transport it to the sweat glands in the skin, whence it emerges to be evaporated for cooling the body.
In circumstances where the air temperature is higher than body temperature, the body can no longer cool itself through radiation, convection, or conduction and must rely solely on the evaporation of sweat for continuing health. On first exposure to the stressful conditions, there is a great deal of discomfort, which varies according to the amount of muscular activity. As adaptation or acclimatization progresses, this discomfort gradually diminishes and disappears after about two weeks.
Acclimatization is generally more difficult in the jungle climates than in hot/dry or desert environments. Two main reasons can be given for this:
- The high humidity of the hot/wet environment is maintained by day and by night, and the higher this relative humidity the more difficult it becomes for sweat to evaporate from the body and cool it.
- Nights in the desert vary from cool to cold, so the body’s
sweating mechanism has some rest. This is not so in the jungle.
A state of acclimatization to the jungle may be transferred to the desert without ill effect, but the reverse is more difficult, for the reasons already mentioned.
Heat acclimatization can be achieved to a considerable degree in the privacy of one’s own home. Commencing three weeks before the intended journey, devote one hour daily to fitness training, and one-and-a-half hours to lying in a bath with the water kept as hot as possible (42°C, 108°F). Staying in the bath for this long may be difficult for the first two days or so, but persevere. As much of the body should be immersed as possible, eyes, nose, and ears only out of the water. This is one of the simplest methods of ‘artificial acclimatization’, but it should only be attempted if you are physically fit.
Age and build
Children adapt to hot environments very quickly and happily, especially thin, wiry, active children who have a large surface area/weight ratio, which facilitates evaporative cooling. The same build is an advantage to adults, but the rule again is ‘the younger and fitter, the faster’. Unfit, plump, podgy, and obese persons represent an increasing order of risk. The elderly and anyone with known heart or circulatory disorders such as high blood pressure and hardening of the arteries should either be dissuaded from facing the stress of a hot climate or, with medical advice, should take special precautions—absence of exertion, travel by sea rather than by air, and as much air-conditioning as possible.
Thirst salt and water
The human thirst sensation is defective where water requirements are concerned. It seems, in general, to account for only about 75 percent of the body’s actual needs in the tropics. Despite a high degree of training in these matters, the British Army has had four times as many cases of kidney or urinary stones directly attributable to inadequate water consumption in the Middle and the Far East as in-home stations. The message for the newcomer is to drink water or watery drinks (beware alcohol, which dehydrates) beyond the point of thirst-quenching. Alternatively, ensure enough intake by drinking sufficient water to produce urine that is consistently pale in color: dark urine or a low urine output are both signs of developing dehydration.
Loss of salt from the body in the sweat has been mentioned above, and this chemical must be replaced if a bodily function is to continue. Salt tablets are often used but can cause vomiting and stomach upsets. The author has put entire regiments on to presalted water with excellent effect, by treating all tea, coffee, cocoa, soup, lemonade (from crystals) as well as all water used in cooking. The required salt concentration is one-quarter of a level teaspoonful (about one gram) per pint or two level teaspoonfuls to each gallon. This concentration is below the taste threshold and must be accompanied by a mixed diet.
Clothing and shelter
The jungle Nudity is the ideal state for the jungle environment, as even the thinnest material can interfere with the required loss of heat by radiation and convection. But sweat can be evaporated from the clothes instead of the skin with the same amount of cooling by either route.
Clothing is usually required, however, not only to satisfy local customs and religions, but also to protect against thorns, cutting plants, and the onslaughts of biting insects. Protective leg and footwear are essential for jungle trekking for these reasons as well as for protection against snake bite and parasitic diseases such as hookworm.
The desert The intensity of the sun in the desert necessitates head and body protection to prevent sunburn, which apart from being extremely painful may hinder the function of sweat glands, thus causing serious illness. Again, the materials used must be the lightest possible, not only in weight but also in color. While color is not important for jungle clothing, in the desert a light or white color will aid the body’s heat balance by reflecting radiant heat away.
Desert clothing comprises loose-fitting long-sleeved upper garments, preferably cotton, with long trousers, to minimize the skin’s exposure to intense solar radiation—until a good tan has developed after strictly graded sunbathing. Here the head requires a broad-brimmed floppy hat to protect forehead and neck before ‘tanning’. The Arab head-dress, the khaffieh (a one- meter square of muslin) is very useful in a variety of ways: it can be wrapped around the face for protection in sand-storms or used as a neckerchief to prevent sunburn under the chin in the vicinity of water (which reflects ultraviolet solar radiation upwards). (See also the next chapter—Sun and the traveler).
Footwear can be as diverse as there are people to have opinions. The author’s preference has been quite simple— boots and puttees for trekking in the jungle and ‘flip-flops’ for rest periods to allow skin and footwear to dry out. The heavy tread of boots provides a warning to jungle denizens such as snakes, who hopefully will ‘slope off.
Desert boots with thick crepe rubber soles and uppers mostly of reversed calf leather, but sometimes of canvas, are preferable to almost any other form of footwear for the desert. A word of caution, however, if you intend to clamber around the very sharp rocks characteristic of some deserts: these require much stouter boots. As in the jungle, desert footwear requires ‘time off to dry out.
Shelter in the jungle environment, from the singleperson poncho or bivouac to permanent buildings, requires a waterproof roof and little else, to take advantage of every slight breeze. Tents and houses should be surrounded by deep run-off systems for the frequent heavy downpours that occur. Sleeping platforms, well above ground level, must be surrounded by mosquito nets. Temporary or permanent shelter in the desert climate should preferably have a double roof (and no corrugated iron sheets, please) to minimize heating of the interior by direct solar radiation.
Air-conditioning Sweat-soaked clothing will chill the wearer rapidly on entering air-conditioned habitation. Carry either a complete change or extra items for such eventualities. Air-conditioned offices are a mixed blessing for many, especially for newcomers to the Far East in Singapore, Bangkok, Hong Kong, and the like. They find that they can work intensively during the day but, on leaving the cool, fairly dry conditions, for the ‘outside world’ they are quite exhausted by early evening. Reliance on alcoholic refreshment is an unwise habit to develop in these circumstances.