what do the two machines do? Who is operating them?

From the text:

"They had this machine. They had two machines, really. One of them slid down into your stomach like a black cobra down an echoing well looking for all the old water and the old time gathered there. It drank up the green matter that flowed to the top in a slow boil. Did it drink of the darkness? Did it suck out all the poisons accumulated with the years? It fed in silence with an occasional sound of inner suffocation and blind searching. It had an Eye. The impersonal

operator of the machine could, by wearing a special optical helmet, gaze into the soul of the person whom he was pumping out. What did the Eye see? He did not say. He saw but did not see what the Eye saw. The entire operation was not unlike the digging of a trench in one's yard. The woman on the bed was no more than a hard stratum of marble they had reached. Go on, anyway, shove the bore down, slush up the emptiness, if such a thing could be brought out in the throb of the suction snake. The operator stood smoking a cigarette. The other machine was working too. The other machine was operated by an equally impersonal fellow in non-stainable reddish-brown overalls. This machine pumped all of the blood from the body and replaced it with fresh blood

and serum."