Carolyn Kunin (off list) "violin d'Ingres" is a French idiom meaning "hobby" - apparently the painter was an excellent amateur violinist, able to
play with his friend the greatest violinist of them all:Paganini. I found in a biography of Chekhov by Rayfield a reference to enemas and lyres in an inscription Ch wrote in a book he gave to a certain Sumbatov...It's on the web. So I guess Man Ray's famous photo is a pun ...

Jansy Mello: I found the reference:Anton Chekhov: A Life (1998) by Donald Rayfield, from where I copied the following, after your inspired hint (online copy p.209):

 

"In November 1889 The Northern Herald saved itself from extinction by printing Chekhov's 'A Dreary Story'. The work made a tremendous impact. Chekhov had found a voice and a viewpoint in his disillusioned professor of medicine [   ] The Petersburg Professor of Medicine, Botkin, died of liver cancer that winter, and Chekhov's work seemed prophetic [   ] Anton proudly inscribed a copy to the playwright Prince Sumbatov:

 

From a successful author who's

Managed to combine and fuse

A sould at peace, a mind on fire,

The enema tube and poet's lyre."

 

How amazing. There's not only Chekhov's the very clear link about how he refers to his two "combined and fused" activities:"the enema tube [clyster] and a poet's lyre" So, Nabokov's mention of "clystère de Tchekhov" is clearly directed to Ch's activities as a physician and unrelated to "Chekhov's Gun" as I'd suggested at first. It isn't depreciative, either!  

 

 The evolution to the image of a hobby (the French for "Violin d'Ingres") in Nabokov's writings (citation needed) may have derived from Chekhov's own the "poet's lyre" in that context. I suppose that the more unusual description of Ada's torso as "lyre" and not "violin" may retain this distant link to Chekhov's lines to Prince Sumbatov.

 

Have you also noticed that there is a Petersburg Professor of Medicine named Botkin - informing that Chekhov's "A Dreary Story" was considered to be prophetic of the other doctor's death?   A Nabokovian kind of literary "Leitmotiv", you think?????

 

Now I'll have to locate and read Chekhov's dreary story to combine it with VN's (always informed about this kind of goings on) crazy scholar in PF and to Ada's physical charms.

 

Thanks Carolyn for keeping the "Nabokov specs" on...