Now the whale spouts fifty or sixty times in succession for just the same reason. It is taking a series of deep breaths so that it may purify all the blood in its body, and be able to remain under water for as long a time as possible without having to rise to the surface for air. And, besides this, there is a most wonderful arrangement in its body which enables it to stay below for very much longer than would otherwise be possible. Inside its chest it has a sort of blood-cistern, so to speak, consisting of a number of large vessels, which contain a great quantity of extra blood, besides that which is circulating through the body. This blood, also, is purified when the whale spouts. Then, when the animal has remained under water for some little time, and begins to feel the want of air, it does not rise to the surface at once, in order to breathe, but just pumps some of the extra blood from this curious cistern into its veins and arteries, to take the place of that which is used up and requires to be purified. This it can do over and over again until all the extra blood-supply is used up too, when it is obliged to rise and spout.
As a general rule a whale spends from ten to twelve minutes in spouting, and can then remain under water, if necessary, for considerably more than an hour.
It is owing to this singular method of breathing that whales can be so easily killed. The object of the hunters is simply to drive them below before they have finished spouting. They do this again and again, and the consequence is that the poor animal soon becomes completely exhausted and falls an easy prey.
You remember, don't you, how the seals are protected from cold, partly by their thick and oily fur, and partly by the layer of fat which lies just under the skin? Well, the whales are protected in much the same way. They have no fur, of course; but the layer of fat, which we call blubber, is always several inches in thickness, and is sometimes as much as two feet; so that the whale is never chilled by living in the water, even when it has to make its way through floating ice.
This blubber has another use as well. When the whale dives to a great depth--and sometimes it sinks half a mile or more beneath the surface of the sea--the pressure on its body becomes enormously great because of the weight of the water above it. If you were to dive to half that depth you would die. But the blubber of the whale is so elastic that it resists the pressure just as a great thick sheet of india-rubber would, so that the animal does not suffer from it in the least.