Variations in intensity have long been recognized as a local or general feature of the distribution of malaria. These variations extend to both place and time. Thus large or small regions may be completely free from infection, a condition that with the passage of time may be either permanent or intermittent. Localities adjacent to these may simultaneously experience malaria in varying degrees of intensity. The local transition of intensity from light to severe may be either abrupt or gradual. In areas of prevalence the incidence of malaria is never static, but undergoes constant fluctuations of varying degree from year to year. Yet despite these fluctuations but few of the communicable diseases are as peculiarly diseases of place as is malaria, while many observations prove that the factor of place exercises its influence over but a comparatively narrow radius.