Periodicity characterizes most and perhaps all physiological changes: The normal contraction and relaxation of muscles, and of protoplasm, the pulsation of the heart, the rhythmic respiratory movements, the periodical sleep during the night, action and repose are the rule, and this applies to thought and other nervous energy. Strongly-marked liberations of vital force occur only after a period of non-action has permitted the storing up of energy, which energy when once strongly and thoroughly discharged cannot immediately be followed by another similar discharge, for which time and opportunity for the accumulation of energy in dischargeable form is requisite.
A periodic fever has, in the fact of its periodicity, a very strong indication that it is necessarily related to periodic changes in the patient, or in those environments of the patient which influence physiological periodicity. Periodic fever is most frequently associated with those diurnal changes in the environment which are known
BAKER HB. MALARIA; AND THE CAUSATION OF PERIODIC FEVER.. JAMA. 1888;XI(19):651–663. doi:10.1001/jama.1888.04360040003002