La Mettrie felt this loss all the more keenly, because it was at the same time the reef on which his fortune was wrecked. This is what happened. During the campaign of Freiburg, La Mettrie had an attack of violent fever. For a philosopher an illness is a school of physiology; he believed that he could clearly see that thought is but a consequence of the organization of the machine, and that the disturbance of the springs has considerable influence on that part of us which the metaphysicians call soul. Filled with these ideas during his convalescence, he boldly bore the torch of experience into the night of metaphysics; he tried to explain by the aid of anatomy the thin texture of understanding, and he found only mechanism where others had supposed an essence superior to matter. He had his philosophic conjectures printed under the title of "The Natural History of the Soul." The chaplain of the regiment sounded the tocsin against him, and at first sight all the devotees cried out against him. The common ecclesiastic is like Don Quixote, who found marvelous adventures in commonplace events, or like the famous soldier, so engrossed with his system that he found columns in all the books he read. The majority of priests examine all works of literature as if they were treatises on theology, and filled with this one aim, they discover heresies everywhere. To this fact are due very many false judgments and very many accusations, for the most part unfair, against the authors. A book of physics should be read in the spirit of a physicist; nature, the truth, is its sole judge, and should absolve or condemn it. A book of astronomy should be read in the same manner. If a poor physician proves that the blow of a stick smartly rapped on the skull disturbs the mind, or that at a certain degree of heat reason wanders, one must either prove the contrary or keep quiet. If a skilful astronomer proves, in spite of Joshua, that the earth and all the celestial globes revolve around the sun, one must either calculate better than he, or admit that the earth revolves. But the theologians, who, by their continual apprehension, might make the weak believe that their cause is bad, are not troubled by such a small matter. They insisted on finding seeds of heresy in a work dealing with physics. The author underwent a frightful persecution, and the priests claimed that a doctor accused of heresy could not cure the French guards.