Recent scientific work, discovery, and application to practical affairs of the results of discovery, in regard to three great obstacles to human life and prosperity illustrate the vital importance to the state of scientific research. The obstacles in question are the diseases known as malaria, yellow fever, and Mediterranean, or Malta fever. It is now twenty-five years since Dr. Laveran, of Paris, discovered that malaria, or ague, is caused by a very minute parasite which exists in the red blood corpuscles of those stricken with the fever, and suggested that it is probably carried from victim to victim by blood-sucking mosquitoes (gnats). Major Ross, of the Indian Army, who has been rewarded for his discovery by the Nobel prize, determined to find out what gnat it is which carries the malaria-germ from man to man, and by most persevering experiment and microscopic examination showed that it is not the commoner gnat or mosquito (Culex), but the spot-winged kind (Anopheles), which alone can spread the malarial infection. But Major Ross is, before everything else, a medical man, and his great purpose has been to apply his discovery to the prevention of disease. Whole regions of the earth’s surface are rendered dangerous, or even uninhabitable, for civilised men by malaria; in other words, by the Anopheles mosquito. Accordingly, Ross set to work to find the best means of destroying these agents of disease. He found that the Anopheles gnat breeds in natural collections of water lying upon the surface of the ground in open country, and not as many common varieties of gnats do, in vessels and cisterns in houses. The pools frequented by the malaria-carrying gnat are small and easily drained. The obvious direction of science, therefore, was to remove or to cover up these pools wherever they were found in the neighbourhood of human habitations. Although Major Ross made his discoveries in India, and although he opened a campaign against malaria by removal of surface pools in the Colonies of West Africa--“the white man’s grave”--twice visiting the chief British settlements--only half-hearted, incomplete measures have been taken, insufficient funds have been expended, and a supine executive and half-incredulous officials have failed to do more than partially reduce the prevalence of malaria in those regions. On the other hand, where intelligent officials have understood and accepted the clear results of science in regard to malaria, the most striking and satisfactory consequences have followed.