题目内容
Why does cream go bad faster than butter？ Some researchers think they found the answer, and it comes down to the structure of the food,not its chemical composition--a finding that could help rid some processed foods of chemical preservatives.
Cream and butter contain pretty much the same substances, so why cream should sour much faster has been a mystery. Both are emulsions--tiny globules (小球) of one liquid evenly distributed throughout another. The difference lies in what's in the globules and what's in the surrounding liquid, says Brocklehurst, who led the investigation.
In cream, fatty globules drift about in a sea of water. In butter, globules of a watery solution are locked away in a sea of fat. The bacteria which make the food go bad prefer to live in the watery colonies of the mixture. "This means that in cream, the bacteria are free to grow throughout the mixture," he says. When the situation is reversed, the bacteria are locked away in compartments (密封仓) buried deep in the sea of fat. Trapped in this way, individual colonies cannot spread and rapidly run out of nutrients. They also slowly poison themselves with their waste products. "In butter, you get a self-limiting system which stops the bacteria growing," says Brocklehurst. The researchers are already working with food companies keen to see if their products can be made resistant to bacterial attack through alterations to the food's structure. Brocklehurst believes it will be possible to make the emulsions used in salad cream,for instance,more like that in butter. The key will be to do this while keeping the salad cream liquid and not turning it into a solid lump.
The significance of Brocklehurst's research is that ______.
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Compared with smart animals, stupid ones are more often immobilized by sleep.
Commercial application of the research finding will be possible if salad cream can be made
Some members of the British government criticized Diana because
Evolution of Sleep
Sleep is very ancient. In the electroencephalographic sense we share it with all the primates and almost all the other mammals and birds: it may extend back as far as the reptiles.
There is some evidence that the two types of sleep, dreaming and dreamless, depend on the life-style. of the animal, and that predators are statistically much more likely to dream than prey, which are in turn much more likely to experience dreamless sleep. In dream sleep, the animal is powerfully immobilized and remarkably unresponsive to external stimuli.
Dreamless sleep is much shallower, and we have all witnessed cats or dogs cocking their ears to a sound when apparently fast asleep. The fact that deep dream sleep is rare among prey today seemsclearly to be a product of natural selection, and it makes sense that today, when sleep is highly evolved, the stupid animals are less frequently immobilized by deep sleep than the smart ones. But why should they sleep deeply at all？
Why should a state of such deep immobilization ever have evolved？ Perhaps one useful hint about the original function of sleep is to be found in the fact that dolphins and whales and aquatic mammals in general seem to sleep very little. There is, by and large, no place to hide in the ocean.
Could it be that, rather than increasing an animal's vulnerability, the function of sleep is to decrease it？ Wilse Webb of the University of Florida and Ray Meddis of London University have suggested this to be the case. It is conceivable that animals who are too stupid to be quiet on their own initiative are, during periods of high risk, immobilized by the implacable arm of sleep. The point seems particularly clear for the young of predatory animals. This is an interesting notion and probably at least partly true.
Almost all the mammals and birds do sleep.
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