Sentence:  [W]e find that the duration and succession of the febrile phenomena constitute five principal groups. ... 2. Fevers which are essentially "continuous" in their course (continued fevers), which exhibit but slight daily differences of temperature during their fastigium or acme, and <WSD>defervesce</WSD> rapidly (by crisis). 
Meaning of the word marked with <WSD> tags:  To experience an abatement or resolution of fever.