Indeed, they, like the seals, are designed to graze on the submarine prairies, and thus destroy the accumulation of weed that obstructs the tropical rivers. “And do you know,” I added, “what has been the result since men have almost entirely annihilated this useful race? That the putrefied weeds have poisoned the air, and the poisoned air causes the yellow fever, that desolates these beautiful countries. Enormous vegetations are multiplied under the torrid seas, and the evil is irresistibly developed from the mouth of the Rio de la Plata to Florida. If we are to believe Toussenel, this plague is nothing to what it would be if the seas were cleaned of whales and seals. Then, infested with poulps, medusæ, and cuttle-fish, they would become immense centres of infection, since their waves would not possess ‘these vast stomachs that God had charged to infest the surface of the seas.’”