PASTEUR (Louis).

Journal des Savants. 1850. Article Chevreul. Autograph manuscript, [ca. 1860], 8 pages in-12 (181 x 115 mm), in modern black half-maroquin folder. Very interesting critical notes on fermentation, bringing together the names of Van Helmont, Chevreul and Pasteur. Pasteur synthesizes here the article of the famous chemist Eugène Chevreul (1786-1889) on Van Helmont, published in 1850 in the Journal des Savants. The Belgian physician and chemist Van Helmont (1557-1644), author of Ortus Medicinæ (1648), was indeed, in spite of his very debatable physiological theories, a great pioneer, who studied gases and discovered gastric juice. Pasteur, reading Chevreul, went straight to what interested him for his own research: ferments and fermentation. It is indeed from 1857, and until at least 1868, that he successively studied lactic, then alcoholic and acetic fermentation. In these reading notes, he summarizes Chevreul's article point by point, in a very precise manner, and ends by underlining certain oddities or errors of the Belgian doctor. Chevreul first recalls that Van Helmont was the first to give ferments the importance that they have been attributed in the economy of living bodies, as well as in that of minerals. He then explains all that is known about fermentation, and states that Van Helmont was a true innovator. He explains his deductions from the phenomena of fermentation that he had observed, notably the leavening of flour that makes the dough rise, which itself becomes leaven, hence this definition of ferment: any body that will convert another into its own matter. Van Helmont came to distinguish between the archaea and the ferment: the one, a single principle that is identical everywhere, acting within the body; the other, more general, acting outside it; from this point on, he was led to relate the cause of molecular actions outside the matter of water, and from this conception came the archaea. Let us add that the ferment, a more general agent than the archea, was another consequence of the same idea. Van Helmont then studied the fermentation of beer, then the role of the ferment in the blood of man: Van Helmont, struck by the idea that the adult man produces per day a quantity of blood which amounts to 7 or 10 ounces, without the weight of this man increasing, attributes to various ferments the faculty to transform this blood into evaporable matter [...]. Continuing this study, Pasteur examines with Chevreul the two classes of ferments distinguished by Van Helmont: one, unalterable, which is a formal being created from the beginning in the form of light, disposed in places where God willed that there should be seeds, and suitable for the development of bodies; the other, alterable and destructible, which develops with the seeds produced by individuals of the same species, and to which Van Helmont still attributes the effect to a property which he calls fermentative virtue, which accompanies the seed during its formation, and disappears or dies as soon as the work is completed. He comes to the ferments-odors, to which he makes play very strange roles. Pasteur then reports two very curious experiments made by Van Helmont and noted by Chevreul: scorpions born from crushed basil, and mice from wheat grains! On the last page, he draws his own conclusion, quite critical, about Van Helmont: M. Chevreul's main purpose is to show that Van Helmont was imbued with the a priori method, that his experiments were made solely, not to enlighten himself by seeking truths of which he was ignorant, but to support opinions conceived a priori which he wanted to establish as truths, even though many of them were errors. A curious proof, Pasteur adds, is that Van Helmont claimed that the first day of creation was in reality only the second, because, counting only two elements, air and water, his system required that they had been created before all the other bodies. This critical analysis is a valuable document on Pasteur's working methods.