The day I was at the Metropolitan Museum of Art, I spent a good deal of time looking at Rembrandt's 1665 portrait of Gerard de Lairesse. I like Rembrandt's work, but mostly I was looking at the painting because doctors who have examined the portrait believe de Lairesse had congenital syphilis.

According to an article by Dr. Horton A. Johnson in the Journal of the Royal Society of Medicine, Dr. J. H. Hanken diagnosed de Lairesse with syphilis in 1913 on the basis of the Rembrandt's painting of him. There are certain deformities that can occur in the face of infants born with congenital syphilis, and Hanken noted these characteristics in de Lairesse's face — his bridgeless  "saddle" nose, for instance. Later doctors agreed with Hanken, and a number of them have written about this diagnosis through art.

I first saw the painting of de Lairesse in the 1980s when I was living in NYC.  I didn't know anything about the medical theories associated with the painting, but I do remember being slightly unsettled by de Lairesse's face when I first saw the portrait. He was obviously an adult, but something seemed childlike in his face. At the same time, there was an aged quality to his eyes. In the end, I settled on the great thoughtfulness in de Lairesse's eyes, and that shaped my final feelings about the painting.

I spent a long time looking at the portrait in the Robert Lehman Gallery last month, and I ended up feeling the same way about the understanding in de Lairesse's face, and depth of feeling in his eyes.

de Lairesse was an artist himself, at least until he went blind at 49, and Johnson's article describes him as "the most celebrated Dutch painter following the death of Rembrandt." He married and had two sons, and after he lost his sight, he wrote and gave lectures. He lived to be 70. I think his life wasn't the easiest at times, though. Johnson quotes from one of de Lairesse's contemporaries, someone named Houbraken, who said that some in Amsterdam found de Lairesse's face "nauseating."

This is what de Lairesse thought he looked like, or at least what showed in his self-portrait from 1670. (In the Uffizi.) From what Johnson's article said, congenital syphilis does sometimes "respect the blood-brain barrier," meaning that some infants born with congenital syphilis don't have spirochetes in their cerebrospinal fluid. That means their nervous systems aren't affected. As he writes, de Lairesse was "fortunate."

Why am I thinking about syphilis? I've been reading about it for a few years as I research my new book, set in 19th century Paris. Flaubert had syphilis, as did Alphonse Daudet and many others. That's all I'll say for now.