Not an easy task on a hot day
Once every year I do not eat or drink for at least 24 hours. Incidentally, many religions demand that followers fast every now and then, but few regulate the uptake of liquids. To go without even plain water is harder than not having anything to eat. Yet, some desert mammals have developed remarkable adaptations allowing them to thrive without having to drink.
One-humped camels, the so-called dromedaries, can go without water for 17 days, losing a quarter of their body weight in the process. However, when given an opportunity “to fill up”, they may drink 100 litres of water in 10 minutes! Contrary to popular belief dromedaries and camels do not, of course, store water in their humps, although their ruminant stomachs contain the liquid. The humps are huge fat reserves, which through oxidation can liberate water and make that available to the body. Glucose and other carbohydrates, too, produce metabolic water, but the loss of water through breathing and sweating tends to be greater than the gain from the oxidation of these food stuffs. Camels and dromedaries partially overcome this problem by elevating their daytime body temperature to about 41°C, so that they need not sweat until it gets really very hot. Moreover, they can tolerate a water loss of 30% (roughly twice that which a human tolerates).
The kangaroo rat, actually a rodent of the North American deserts and not at all a marsupial even though it hops like one, hardly ever drinks. It also lacks sweat glands completely and conserves water by leaving its underground burrow only in the cool of night to nibble on some grass seeds. Its kidneys are extremely efficient and concentrate salts and urea to much higher levels than those of humans can do. But even the kangaroo rat cannot help developing a terrible thirst after eating protein-rich soy beans, for protein-rich food on account of its amino acid contents, results in high amounts of urea, which has to be flushed out of the system with water.
An animal that still loses heat to the environment (even if the ambient temperature soars to 40°C in the shade) is the Oryx antelope, an animal of the African and Arabian deserts. This animal operates with a normal blood temperature of 44.5°C and starts sweating and panting only when the temperature exceeds 46°C: it deserves the prize of the champion non-drinker amongst the larger mammalian species. In order to keep a cool head in spite of the heat it has to function in, the Oryx pre-cools its blood in the moist nasal epithelium before allowing its “air-conditioned” blood to flow around the brain through an intricate meshwork of fine capillaries.
Should by now you have become a bit thirsty (which would not surprise me) then I suggest a hot drink. On a warm day nothing beats hot tea and lemon, for that tells the body to increase the liberation of sweat and that, through its evaporation, will actually cool down the body more efficiently than imbibing ice-cold beverages! And should you happen to be in Japan on a hot day and felt like sweating, why don’t you try that popular and tasty soft drink available from any food store or vending machine in the country: Have a “Sweat” – “Pocari Sweat” to be precise.
© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2016.
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