to participate in defending their own health.

自己参与到保卫自身健康的运动中来
Let me give you an example of a simple technological improvement.

我给大家举个科技进步的很简单的例子
It might be hard to recognize when you first look at it but--

刚看到大家可能认不出来
and I'm talking about some very humble movements that have

我现在讲的是一个很简陋的东西
enormous political and medical consequences.

但在政治上医学上有着巨大的影响
What we're looking at is a sewer main,

我们现在看到的是一截污水干管
and these were established

在那个时期
--under the soil of cities in this period,

这些都被安装在城市地下
and one of the technological inventions

其科技发明之处之一在于
--was to make the sewers egg shaped,

使下水道呈蛋形
so that you would maximize the flow and they would be self-cleaning

这样可以使流量最大化并具有自我清洁功能
and they would drain most efficiently.

也会最具效率地排空污水