"Méry became closely associated with the comparative-anatomical work led by Claude Perrault and J.-G. Duverney. As a member of this group, Méry made contributions to their joint publications, in which each man’s specific contributions usually cannot be determined. Méry worked closely with Duverney until about 1693, when their differing interpretations of mammalian fetal circulation estranged them. The coolness that resulted was apparent to Martin Lister, when he visited Paris in 1698. Méry probably did more to retard than to aid the understanding of this problem. Méry claimed that the blood flowed from the left to the right through the foramen ovale in the interatrial septum. This view was prevalent enough that Haller look time to refute it. Méry initially formulated his theory from a false analogy between a tortoise heart and a fetal mammalian heart. Ultimately he based his theory of fetal circulation on a comparison of the cross sections of the pulmonary artery and the aorta, concluding that not all of the blood passing through the pulmonary artery and returning to the heart by the pulmonary vein could pass into the aorta. Instead, he thought, a portion of that blood passed through the foramen ovale from the left to the right side of the heart.

"Méry erred in assuming that the cross section of an artery is the only factor determining the amount of blood that can flow through it. He compounded this error by his method of measuring the relative cross sections of the arteries. He may have used fresh preparations for his measurements on cows and sheep. For those on human beings, he probably used preserved specimens, dried ones as a rule. The results were inconsistent at best. For example, Martin Lister described a fetal heart that he saw in Méry’s collection which had no valve for the foramen ovale, and which was open in both directions and had a diameter nearly equal to that of the aorta. For two decades numerous arguments were presented on both sides of the controversy between Méry’s views and the traditional views dating back to Harvey and Lower. Méry held his views against all opposition to the end" (DSB). See Kenneth J. Franklin, “Jean Méry (1645–1722) and His Ideas on the Foetal Blood Flow,” in Annals of Science, 5 (1945), 203–338.

Frère Jacques Beaulieu, the work of which the first part of Méry's book refers, was a notorious quack travelling lithotomist.