On this day we celebrate the feast of Sts. Cosmas & Damian, third-century twins, doctors, martyrs.
There are other saints who were twins: Benedict and Scholastica, of course; Florus and Laurus,  stonemasons who were martyred in Illyricum and are venerated as patrons of horses; and Gervasius and Protasius,  patrons of haymakers.
There are twins in Genesis: Jacob and Esau, of course; Uz and Buz; and Muppim and Huppim. In the New Testament we read of Tryphaena and Tryphosa; and we read of Thomas the Apostle, Doubting Thomas, Thomas the Twin. Whose twin was he? Some believe he was Jesus' twin.
For information about all those twins and about Castor and Pollux, the Gemini (by jiminy), see The Cult of the Heavenly Twins,  by James Rendel Harris, Cambridge University Press, 1906. Search terms: Edessa, horses, Castor, Cosmas, Thomas, etc.
"According to the detailed and colourful legend Cosmas and Damian were twin brothers born in Arabia who went to study the sciences in Syria. Once qualified they went to Aegeae on the bay of Alexandretta in Cilicia. Here they practiced medicine without accepting fees from their patients and were widely known and respected for their charity and for their integrity as Christians."
"Their cult, which enjoyed enormous popularity in the early medieval West, illustrates both the willingness of Christianity to absorb the ancient tradition of professional medicine and its ambivalence about this act of appropriation. In his poem on the arrangement of a library, Isidore of Seville ranged Cosmas and Damian alongside Hippocrates and Galen as great medical sages; so does the poem on medical ethics included in the Lorsch Leechbook."
--Medieval Medicine: A Reader,  edited by Faith Wallis, University of Toronto Press, 2010. Search term: Cosmas. See pages 62-66.
Cosmas and Damian, doctors without borders, "went about the cities and provinces healing the sick by the art of medicine and expelling demons." They cured animals, as well as people, including a camel who "had a foot that had been broken by a devil."
They "treated every infirmity and every debility among the people and never demanded a fee." They were anargyroi--without money. When a patient "adjured" Damian to take three eggs "in the name of the Almighty," Cosmas "gave an order to his household that after his death, they should not lay his body beside that of his brother Damian." But the Lord appeared to Cosmas and explained that Damian "'was adjured in the name of God, and this is no sin.'"
So powerful was the story of the martyrdom of Cosmas and Damian, that "the text itself, if read over the bed of a sick person, was supposed to be therapeutic."
To read the therapeutic passio, see pages 64-66 in Medieval Medicine.
The names of Cosmas and Damian may be mentioned in the First Eucharistic Prayer, but it is optional. Like Gervasius and Protasius, they are invoked in the Litany of the Saints.
"VIVA SANTI COSMA E DAMIANO!"
Click here  for a festival held earlier this month in honor of The Healing Saints Cosmas & Damian at Cambridge, Massachusetts. Bobby Rydell was one of the performers. The statues of the twins were bedecked with money. (In 1988 the Smithsonian Institute asked the Society of Saints Cosmas & Damian to recreate their annual festival on The Mall.)