Doctor
Doctors are one of the new features in Assassin's Creed II. Found on the streets of every city in black robes and mask with a beak-like shape, they can either refill Ezio's Health Bar for a fee, or sell him Medicine that can be carried and used later. They also sell him vials of poison for his Poison Blade.
Doctors are perhaps the most vital service in AC2 as they sell Medicine to heal after fights or after falling from height.
Appearance and historical relation
The doctors in Assassins Creed II, as usual for their kind after one of the deadliest pandemics in human history (known as The Black Death ), dress in a long black cloak covered with a coating of wax, and a very primitive beak-shaped gas mask, or without a beak-shaped gas mask.
The Black Death plague peaked in Europe during the 14th century and is said to have killed 30% to 60% percent of Europe's population. That reduced the world's population from an estimated 450 million to between 350 and 375 million in 1400
Heal
Doctors can replenish all of your health by paying him a paltry sum of 50 florins. The price from the Doctor in Monteriggioni for his healing services, however, decreases as you renovate his stall.
Apothecary
Medicine
Doctors sell Medicine (75ƒ each) that acts as a healing item that can be carried with you anywhere you go. The number of Medicine vials you can carry at one time increases when you upgrade your Medicine Pouch from a Tailor. In game, the medicine itself is said to be smelling salts that act as painkillers. This is the only way to heal yourself, other than an automatic healing at the start of most memories.
Poison
Doctors sell Poison vials for a sum of 175 florins. When Ezio asks Leonardo why Doctors would sell Poison, he replies that, "when given in high doses, that which heals can kill". Poison is available only after upgrading Ezio's Hidden Blade with the Poison Blade. The Poison is useful for players who do not want to assassinate a target quickly or for those who rather create a distraction. Poison is a potent weapon. Like the Hidden Blade, it offers one-use kills, but it is easily used on any target and runs less of a risk of Exposing the player as you can use the Blade and be several streets away and even in another District by the time the target has died, where as with the Hidden Blade, after an Assassination, the player has only five seconds before the body audibly hits the ground.
The Poison Blade is good when the player need to assassin a target with out being noticed. Also if the target has a body guard, poison the guard, he will most likely to hit the target when swinging his weapon around violently. (95% it will work) The target should come close to the guard and say something like: "what are you doing". Then the guard takes the kill.