The fighting of the species that breed on the extensive salt-marshes in many regions is a larger and more difficult problem, but as it is a matter that usually concerns large communities, sometimes whole states, it can be dealt with on a larger scale. The very excellent results that have been accomplished in New Jersey and on the San Francisco peninsula, and in a smaller way in other places, show what may be done if the community goes about the fight in an intelligent manner. In the fight in New Jersey hundreds of acres of tide-lands have been drained so that they no longer have tide pools standing where the mosquitoes may breed. When it is impracticable to drain them the pools may be sprayed occasionally with kerosene. The value of the land that is reclaimed by a good system of draining is often enough to pay many times over the cost of draining, thus the mosquitoes are gotten rid of and the land enhanced in value by a single operation. CHAPTER VII MOSQUITOES AND MALARIA Ever since the beginning of history we have records of certain fevers that have been called by different names according to the people that were affected. As we study these names and the various writings concerning the fevers we find that a great group of the most important of them are what we to-day know as malarial fevers. Not only are these ills as old as history but they have been observed over almost the entire inhabited earth. There are certain regions in all countries where malaria does not occur, but almost always it will be found that other regions near by are infected and it very often happens that these infected regions are the most profitable parts of the land, the places where water is plentiful and vegetation is luxuriant. Indeed the coincidence of these two things, low-lying lands with an abundance of water, particularly standing water, and malaria has always been noted and gave rise to the earliest theories in regard to the cause of the disease. For instance, we find some of the very early writers emphasizing the point that swampy localities should be avoided for they produce animals that give rise to disease, or that the air is poisoned by the breath of the swamp-inhabiting animals. These views of the origin of the fever prevailed until about the beginning of the eighteenth century when the recently discovered microscope began to reveal the various kinds of animalculæ to be found in decaying material. In 1718 Lancisi held that the myriads of insects, particularly gnats or mosquitoes, that arose from such swampy regions might carry some of these poisonous substances and by means of their proboscis introduce them into the bodies of the people, and although he had made no experiments to test the assumption he did not consider it impossible that such insects might also introduce the smallest animalculæ into the blood. It took almost two centuries of study and investigation before this guess was proved to be right.