According to one of his American students, J. Alden Weir,
“I went into the dissection room and saw Mr. Bonnat with the Prof. [Gerome]. They had just received a subject, and a the opposite side of the room I saw an immense cross, but thought nothing. Bonnat said he had not much time to stay and wanted the gendarme to hurry up so two of these soldiers and a hired man took the subject out of the room, brought the cross out and laid it on it.
It was then whispered about that Bonnat had a commission to paint a crucifixion, had bought the subject, and had the cross fixed, so as to be able to study the action of the muscles. Some of the students, hearing what was up, crowded in; this attracted Bonnat’s attention, and he got the gendarme to close the door and lock it.
We went back to the lecture room where we draw the bones, and while sitting there we heard the nails driven in. We finished; Mr. Blackman and myself went out together after all had gone.
At the door we met a guardian and bribed him to let us see the subject, which he did, and standing up against the wall was the large cross with the subject crucified on it, a horrid sight; but it shows how these French artists believe in truth.”
--from The Lure of Paris: Nineteenth-Century American Painters and Their French Teachers, by H. Barbara Weinberg