英国学生科学读本 第91期:牛奶及用途(1)

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　　Every child likes to drink new milk. 每个孩子都喜欢喝鲜牛奶。

　　How pleasant it smells and how sweet it tastes! 那香浓的味道, 甜美的滋味是多么诱人！

　　Do you not want to know something about this useful liquid? 对于这样一种极为有用的饮品, 你肯定想要了解更多吧?

　　Nearly all the milk we use comes from the milk-bag or udder of the cow. 我们喝的牛奶几乎全部来自奶牛的乳房。

　　But people also drink the milk of other animals, such as the goat, the ass¹, and the camel. 不过, 人们还饮用其他动物的奶, 例如羊、驴以及骆驼。

　　All these animals have a plentiful² flow of milk, which is intended for their own young ones. 所有这些动物都拥有非常充足的奶量, 因为它们需要为幼仔提供足够的营养。

　　Animals which bring up or nourish their young on milk are called mammals. 依靠奶来抚养后代的动物就叫做哺乳动物。

　　Milk is an excellent food. 奶是一种很好的食物。

　　It has been called a "model " food, for it contains just the things that we need to nourish our bodies, and these are mixed in just the right way. 它被称作“模范”食品, 因为其中包含了人体所需的营养, 而且成分的搭配也很合理。

　　Milk is a white fluid a little heavier than water. 奶是一种白色流体, 比水稍重。

　　We call it a fluid because it will flow. 之所以称之为流体, 就是因为它会流动。

　　All liquids are fluids, and so are all gases; for both liquids and gases will readily flow from one place to another. 所有的液体都可以流动, 气体同样如此, 因为液体与气体随时都可以四处移动。

　　But solids, such as wood and iron, do not flow. 然而, 诸如木头与铁块这样的固体却不会流动。

　　Of what is milk composed? 奶是由什么构成的呢?

　　Let your new milk stand all night in a glass jug³, say twelve inches in height; 我们把新鲜牛奶放进一只高度为十二英寸的玻璃杯静置一晚；

　　then in the morning you will see—or you ought to see—a rich, yellowish-white layer of cream one inch in thickness on the top of the milk. 到了清晨你就能够（也应该）看到牛奶最上方出现了一层一英寸厚的黄白色粘稠奶油。

　　If your jug is six inches high, you should have a layer of cream half an inch thick.  如果杯子高度为六英寸, 奶油的厚度就应该在半英寸左右。

　　This cream contains thousands of tiny balls of milk-fat, each ball having its own covering or skin. 这层奶油中包括成千上万颗乳脂小球。

　　These balls rise to the top because they are lighter⁴ than the rest of the milk, just as a cork⁵ rises to the surface of water. 这些小球之所以上升到杯子的最上层, 是因为它们比牛奶的其他成分要轻, 这就好像是软木塞能够漂浮到水面一样。

　　People skim off the cream and put it into a kind of wooden tub or barrel called a churn, 人们将这层奶油分离出来, 然后放入名为搅乳器的木桶之中,

　　in which they beat and dash it about by moving a plunger up and down, or by turning a handle. 通过上下移动活塞或者转动把手来搅拌奶油。

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