Please, have a look at this picture:

It represents the Medicine. At the bottom you see a swan and a cock. The cock was sacred to Asclepius and should be one of his symbols here. But what about that swan sitting on an open book? Currently I don't know where this picture came from, but I can ask for information, if it helps. A friend of mine asked me for a suggestion about its iconographic meaning, but I have no idea.

edited to add: It's a fresco of the 18th century, a cycle of paintings actually, on the wall of the former Aula Magna (Great Hall) of the university of Pavia. Here a view:

I was fancying that maybe in some way the rooster on the closed books represents the practical side of the medicine, the practice, while the swan on the open book the studying, the theory (but it's just a fantasy of mine). Intriguing by the way that first comes the open book, and then the closed ones.