The chief diseases, both acute and chronic, of tropical countries--those which formerly caused such ravages among the white settlers, and gave rise to the prevalent theory that Europeans can live only in the temperate zone--are all microbic in origin, and consequently in great measure preventable. We cannot expect, of course, to see them absolutely wiped out of existence; but their sting may be extracted by means of an improved public and private hygiene and other prophylactic measures. A comparison of the healthfulness of the West India Islands under enlightened British rule with that of the two under Spanish misrule shows what can be done by sanitation to convert a pest-hole into a paradise. Indeed, as Dr. L. Sambon, in opening the discussion, well said, sanitation within the last few decades has wrought wonderful changes in all tropical countries as regards health conditions, and the changes in some places have been so great that regions once considered most deadly are now even recommended as health resorts. Dr. Patrick Manson, than whom there is no greater authority on the pathology of equatorial regions, began his remarks with the confession that in former years, under the influence of early training, he shared in the pessimistic opinions then current about tropical colonization by the white races. In recent years, however, his views on this subject had undergone a complete revolution--a revolution that began with the establishment of the germ theory of disease. He now firmly believed in the possibility of tropical colonization by the white races. Heat and moisture, he contended, are not, in themselves, the direct cause of any important tropical disease. The direct causes of ninety-nine per cent, of these diseases are germs, and to kill the germs is simply a matter of knowledge and the application of that knowledge--that is to say, sanitary science and sanitation.[17]