A cleansing medicine by a certain roughness or nitrous quality, carries away the compacted filth with it.
This also is the difference between cleansing and discussing medicines, the one makes thick humours thin, and so scatters them, but a cleansing medicine takes the most tenacious humour along with it, without any alteration.
Besides, of cleansing medicines, some are of a gentler nature, some are more vehement.
These are not known one and the same way; for some are sweet, some salt, and some bitter.
The use of cleansing is external, as the use of purges are internal.
They are used to cleanse the sanies and other filth of ulcers, yea, and to consume and eat away the flesh itself, as burnt Alum, precipitate, &c.
When these must be used, not only the effects of the ulcers, but also the temperature of the body will tell you.
For if you see either a disease of fulness, which our physicians call [Plethora] or corrupted humours which they call [Cacochyma] you must empty the body of these, viz. fulness by bleeding, and corrupt humours, or evil state of the body, by purging before you use cleansing medicines to the ulcer, else your cure will never proceed prosperously.
