In regard to the possible authors of the crime, some accused the Dutch, against whom the Treaty of Dover was directed; others accused Monsieur himself and the Chevalier de Lorraine. In either case, the historical interest of the problem is very great; the popular imagination heightened it through the magnificent commentary with which Bossuet embroidered the death of the beautiful princess; and it has been enhanced by all the efforts made for more than a century past to solve it. 'For fifty years and more,' writes one of the masters of modern erudition, M. Arthur de Boislisle, 'the question has been more closely studied, and the evidence weighed with more care, at least by impartial and serious writers familiar with the documents of Louis XIV's reign or with scientific problems. But it happens that some have abstained from giving a decisive verdict, and others have varied between poison, in which Walckenaer, Paul Lacroix, and François Ravaisson very firmly believed, and death by accident or disease, accepted by Mignet, Loiseleur, and Littré; with the result that the question has become darkened rather than illuminated between conclusions diametrically opposed, but coming from men of equal authority.' Monsieur de Boislisle himself refrains from stating any conclusion, and recently we have Doctor Legué, a specialist, in his interesting book, _Médecins et Empoisonneurs_, devoting a new study to the question, and endeavouring to prove that Madame was poisoned by corrosive sublimate. Thanks to a minute study of the documents, guided by the work of Monsieur de Boislisle we have just quoted, thanks above all to the skilful guidance of two masters of modern science, we arrive, as will be seen by and by, at an indisputable solution. I In accordance with the first principle of historical criticism, it is important at the outset to determine exactly the value of the sources whence we may derive particulars serviceable to our investigation. The sources are divided into three well-marked categories--(1) The reports of the physicians and surgeons; (2) the accounts of the persons who were able to approach Madame in her last moments, or were in a position to hear authoritative descriptions; (3) the official correspondence of the courts of London and Paris. The first category presents to us five reports of the post-mortem examination:-- (_a_) The official report signed by the fifteen physicians and surgeons, French and English, who were present at the autopsy. (_b_) The _Account of the Illness, Death, and Autopsy of Madame_, by the Abbé Bourdelot, physician. Bourdelot was one of the French physicians present at the post-mortem. (_c_) The report of Vallot, physician to the late queen-mother. Vallot was regarded as one of the most eminent physicians of his time. He was present among the French doctors at the autopsy. His report was officially carried to London by the Marshal de Bellefonds.