I came across a portion of Myth a while back. It said something like gorgon's blood taken from one side of the body can heal any malady but the other side can kill instantly. Who is this writing (for multiple sources- Who are these writings) attributed to?
The writing, entitled the Bibliotheca, "Library," used to be attributed to the Athenian historian Apollodorus, but, as Wikipedia says, 'that attribution is now regarded as false, and so "Pseudo-" was added to Apollodorus' so that one now reads about 'Pseudo-Apollodorus' (pseudo meaning 'false') penning that work, whose actual author is apparently unknown.
The specific passage to which you are referring is Bibliotheca 3.10.3, which relates the career of the physician Asclepius:
Having become a surgeon, and carried the art to a great pitch, he not only prevented some from dying, but even raised up the dead; for he had received from Athena the blood that flowed from the veins of the Gorgon, and while he used the blood that flowed from the veins on the left side for the bane of mankind, he used the blood that flowed from the right side for salvation, and by that means he raised the dead.
I found some who are reported to have been raised by him, to wit: Capaneus and Lycurgus, as Stesichorus says in the [book] Eriphyle; Hippolytus, as the author of the Naupactica reports; Tyndareus, as Panyasis says; Hymenaeus, as the Orphics report; and Glaucus, son of Minos, as Melesagoras relates.
The Egyptian writer Nonnus, in Book 44 of his epic the Dionysiaca, says that one of the Erinnyes collected some of Medusa's blood shortly after the Gorgon was slain.