[... the most illustrious physicians say] that being feverish or being chilled, we perceive in our illnesses, not the sensory nerves or the heated flesh themselves, but the fluids of both blood and breath.[1] Now, since the sensitive faculty resides primarily in flesh and nerves, it is plausible that, since fluids are hard to control (I mean breath and blood), and are juxtaposed with the sensory parts, we apprehend them by touch, just like the air which is heated or chilled [...] even if fever takes hold of the solid [parts] themselves, since they are warmed not evenly, but unevenly. For there are some parts that are [warmed] according to nature, and others contrary to nature. Sometimes what is [warmed] according to nature prevails over what is disposed contrary to nature. For it is impossible for a bad temperament to become uniform. But those who are possessed by a chronic fever, that is those whose solid [bodily] parts have become fevered (a bad temperament in them arising uniformly throughout the whole of the solid [bodily] parts), take no awareness of warmth in themselves, because warmth is uniform through all the parts, and one part is not active and the other part passive.
Ailment is different from illness. Search also under [the entry] 'ailment'.[2]