As the title of this treatise suggests, it focuses on the differences of fevers. The term "difference" belongs to Aristotelian logic. By differences, we mean the specific variations, the modifications that are applied to a common genus of things, in this case, fevers, and give us their particular species. For example, if we apply the specific difference of logic to the general category of animals, the particular species of human arises, since a rational animal is a human.
The essential characteristic of all fevers, which determines their essence, is the abnormal increase in the temperature of the heart, which, according to Galen, regulates the temperature of the entire body. Based on the quantity of this heat, fevers are divided into small and large. [...]

(from the introduction of the book)