Dear Cecil: I've heard coconut juice is almost identical to human blood plasma, and has been used as a plasma substitute during wartime. I asked a friend from Vietnam who lived there during the war about this, and she was very matter-of-fact about the use of coconut juice as a substitute for blood plasma during the war by Vietnamese soldiers (on both sides). She told me when they expected a big battle, they would gather coconuts in preparation for medical use. Has there been any research into this? Is it safe and effective? Are there any ill effects? Mickey B., Las Vegas, NV

Cecil replies:

Well, one drawback is you look like something out of Gilligan’s Island. A photo in a medical journal shows a coconut hanging from an IV stand with a standard blood transfusion tube attached. And really, coconut water isn’t all that much like plasma. But generally speaking, coconut transfusions are legit.

Coconut water can be used for a variety of medical purposes, one of which is intravenous rehydration. A 2000 report tells of a stroke patient in the Solomon Islands who was too ill to drink or use a nasal tube but was successfully rehydrated with a coconut-water IV when no other fluids were available. Emergency coconut IVs were reportedly used by the British and Japanese during World War II, and they’ve been clinically tested on humans several times to see how well they’d be tolerated. Answer: overall, pretty well.

Remember, we’re talking about coconut water, the liquid found inside a young coconut, not coconut milk, which is made from grated coconut meat. Coconut water can’t actually replace blood plasma; chemical analysis indicates it’s closer in makeup to intracellular fluid. It’s usually sterile, and when mixed with plasma it behaves like saline solution. It’s got fewer electrolytes in it than our bodies are used to and too much potassium, so it’s not an ideal rehydration fluid. But it works in a pinch.

Another surprising use for coconut water: Remember when you were young and your mother told you if you ever lost a tooth on the playground to keep it in milk until you got to the dentist? According to a recent study in the Journal of Endodontics, coconut water is even better than milk for keeping a tooth viable. Where you’re going to find some on short notice at a playground I have no idea. But if you’re ever roughhousing in the Solomon Islands, keep it in mind.

Dear Cecil:

I work in a store that sells space heaters, among other things, and now that winter is upon us I have an important question. Are sealed-oil space heaters more efficient than the old hot-wire-and-fan kind? All this time I’ve been telling my customers they were, but lately I’ve begun to wonder. While the oil heater is warming up, am I losing the efficiency that returns when the oil reaches operating temperature?

— Dennis Miller

Cecil replies:

Confusing subject. Many reason as follows: oil space heaters have more thermal mass and so remain warm even when their internal heating element cycles off. Therefore, they’re more efficient.

False. In the big-picture sense, all electric heaters have equal efficiency: for a given amount of electricity, they produce the same amount of heat. What’s different is the type of heat and how it’s distributed. The issue isn’t the efficiency of the heater itself, but rather the best method of heat delivery for the situation.

A radiant hot-wire heater is designed to directly heat nearby surfaces (skin, for instance) through thermal radiation, which is good if, say, you’re trying to get warm quickly in a large, drafty room. But it also gives you very uneven heat, in both the spatial and temporal sense. While the heater is running, the near side of you roasts while the other remains cold, and once it cycles off, things quickly cool down. An oil heater works mainly by convection: it’s designed to warm up a mass of air that will then circulate through the room.

Which is better? Depends. If your goal is to heat a smallish, well-insulated space over a long period, a convection heater will distribute warmth more uniformly, making the room more comfortable. If your goal is to heat you, a radiant heater may make more sense. You can focus the heat on yourself rather than waste it warming a lot of empty space.

True, an oil heater in a confined space, such as in the footwell under a desk, arguably would accomplish the same thing, so let’s not get hung up on details. The main thing is this: if you’re trying to save money, heat the least amount of space possible while still staying warm. The best solution I’ve found? A fan-driven electric foot warmer. It effectively heats only about half a cubic foot of air, but if that’s where your feet are, that’s all you need.

Cecil Adams

Send questions to Cecil via cecil@straightdope.com.