Salt is as necessary to life as water. In many areas of Africa people once drank the urine of animals because they had no other source of salt. Without salt, human beings die.

    The human body demands that the amount of salt in the blood always stay the same. When the body does not get enough salt, it protects itself by letting less salt leave the body in. urine and sweat. But it cannot reduce this output to zero. Some salt is always escaping. On a completely saltless diet, like that of some people in Africa, the body steadily loses small amounts of salt through the kidneys and sweat glands. It then tries to adjust to this loss by speeding up its secretion of water. In this way, the body attempts to keep the amount of salt in the blood at the necessary level. The result is a slow drying up of body and, finally, death. The person dies of thirst.

    In cases where there is little or no water to drink, the body tries to do the opposite thing.
Again, it must keep the salt level in the blood constant.Because it has little water, it attempts to stop water from leaving the body and to increase its secretion of salt. But, as with the escaping salt, it cannot be completely successful. Some water still leaves and the person eventually dies of thirst. In short, the body's normal needs for salt and for water are both parts of the same important need to keep the salt level in the blood constant.

和水一样，盐也是生命不可缺少的物质。非洲很多地区的人都曾经饮用过动物的尿液，因为他们没有别的盐的来源。没有盐人们就会死亡。

人类的身体要求血液中盐分的数量总是保持一致，当身体没有足够盐分的时候，它会通过让尿液和汗液排放更少的盐分来保护自己。但是它不能把输出量减少为零。一些盐分总会流失掉。完全没有盐分的饮食，就像一些生活在非洲的人，他们的身体会通过肾腺和汗腺缓慢地失去少量的盐分，然后再通过加速分泌水来调节这个损失。身体通过这种方式尽量让血液中的盐量保持在一个必要的水平上。这样调节的结果就是人们的身体慢慢地干涸，最后死去，也就是渴死。

一旦人们有很少或没有水喝，身体就会做出相反的反应。它必须保持血液中盐分的稳定。因为几乎没有水分的时候，身体会试图阻止水离开它并且增加盐分的分泌。但是由于要流失盐分，也不能完全成功地阻止水分离开。一些水还是会流失，最终导致人们渴死。简而言之，身体正常需要的盐分和水分对于保持血液中盐分的水平不变是同样重要的。