Voynichese is a numeric cipher?

[ololololo]

Such liberties are possible, but they do not take place, and when you write a book about medicine, you rather sign the fire as fire, because you do not need to play the reader.

I can't agree, if this is a book about medicine and not a kindergarten primer, I'd say it makes little sense to draw fire and label it as "fire". Certainly the reader knows what fire looks like.

In a medical book of the time one example could be a text talking about how humors relate to elements, in which case labelling elements for their corresponding humors would be informative. Then fire would be labelled something like "bile", air as "blood", water as "phlegm", etc.

In reality I don't believe we can expect the fire image to be literally labelled as "fire". It is possible, but it's far far from certain.

That's true. If we accept my assumption that the balneological section is an anatomy, then there can be no "fire" or "earth" there, because this is not an alchemy textbook. It's most likely an allegory for humors, as you have noticed. However, I believe that it is more important to identify the meaning of the word than to accurately identify what the author drew.