(b. Ormonville-la-Petite, Manche, France, 12 December 1868; d. Paris, France, 15 February 1938)
zoology, general biology, tropical medicine.
Mesnil, whose family had been farmers in Normandy for several generations, attended the school in his village. One of his uncles, a physician in the navy, recognized Mesnil’s exceptional ability and arranged for him to enter the lycée in Cherbourg and then the Lycée Saint-Louis in Paris. At the age of eighteen he was accepted by both the École Polytechnique and the École Normale Supérieure; he chose the latter because of the interest in natural history he had developed during his boyhood. He passed the agrégation in the natural sciences in 1891 and obtained his doctorate in 1895 with a work on the resistance of lower vertebrates to microbial invasions. After passing the agrégation he spent several months at universities in central Europe. Upon returning, he entered the Institut Pasteur and remained there throughout his career. While serving as assistant and secretary to Pasteur, he began to work in Metchnikoff’s laboratory, where he acquired experimental technique. Mesnil became agrégé préparateur in 1892, laboratory director in 1898, and professor in 1910.
Mesnil’s work was varied, much of it oriented toward general biology; important memoirs dealt with systematic, ecological, and ethological zoology. For more than thirty years, during summer vacations Mesnil had the opportunity to study—first alone and then, beginning in 1914, with his brother-in-law Caullery—the fauna of St. Martin Cove, near the Cap de la Hague, and of the neighboring coasts. This research resulted in the description of many new genera and species of annelids, crustaceans, enteropneusts, turbellarians, Orthonectida, and protozoans. A great number of investigations were devoted to the annelid polychaetes—to their morphology, in order to establish their phylogenetic relationships; to their sexual maturity (epitokous forms); and to their asexual reproduction (schizogenesis, regeneration). Mesnil, who was interested in parasitism, discovered that condition in the Monstrillidae. With Caullery, he described Xenocoeloma brumpti, a parasite of Polycirrus arenivorus; the two scientists furnished a precise analysis of its morphology, of the penetration of the larva into the annelid, and of its complex development. They also studied isopod parasites of sea acorns and spheromes; Fecampia (turbellarian rhabdocoeles that are internal parasites of crustaceans); and the Orthonectida and their life cycle.
Alone or with Caullery and A. Laveran (the latter discovered the hematozoon of malaria), Mesnil examined the parasitic protozoans: gregarines, coccidia, Myxosporidia, Microsporidia, infusoria, and flagellates. From 1900 to 1916 Mesnil was concerned especially with the trypanosomesand trypanosomiases; chemotherapy, determination of the species, experimental constitution of heritable strains, infectious power and virulence, reactions of the organism, and the resistance of certain strains to medicines and serums. He was also interested in natural and acquired immunity. He and Laveran devised the test that bears their names for detecting the specific identity of the trypanosomes.
Mesnil reported on many works in microbiology and general biology for various French journals. With G. Bertrand, A. Besredka, Amédée Borrel C. Delezenne, and A. C. Marie he founded the Bulletin de l’Institut Pasteur and he was also its editor. In 1907 he participated in founding the Société de Pathologic Exotique, of which he was secretary-general (1908–1920), then vice-president and president (1924–1927).
Mesnil belonged to the Académie des Sciences (1921), the Académie de Médecine, and (as founding member) the Académic des Sciences Coloniales. He was a commander of the Légion d’Honneur. In 1920 he received the Mary Kingsley Medal of the Liverpool School of Tropical Medicine, and in 1926 C. M. Wenyon dedicated his Textbook of Protistology to Mesnil Among Mesnil’s students were E. Roubaud, E. Chalton, A. Lwof, and S. Volkonsky.
Mesnil’s learning was prodigious and his memory legendary. Kind and easily approachable, he gave advice and support to everyone. The archives of the Académic des Sciences contain his portrait and autograph manuscripts.
I. Original Works. A complete bibliography is in Titres et travaux scientifiques (1893–1920) (Laval, 1921). Mesnil’s major book was Trypanosomes et trypanosomiases (Paris, 1904; 2nd ed., enl., 1912), written with Laveran.
His early articles include “Sur la résistance des vertébrés inférieurs aux infections microbiennes artificielle,” his doctoral diss., published in Annales de l’Institut Pasteur, 9 (1895), 301–351; “études de morphologie externe chez les annélides. I. Les spionidiens des côtes de la Manche,” in Bulletin scientifique de la France et de la Belgique, 29 (1896), 110–268; “… II. Remarques complémentaires sur les spionidiens. La nouvelle famille des disomidiens. La place des aonides” and “… III. Formes intermédiaires entre les maldaniens et les arénicoliens,” ibid., 30 (1897), 83–101 and 144–168; “… IV. La famille nouvelle des levinséniens. Révision des ariciens. Affinités des deux families. Les apistobranchiens,” ibid., 31 (1898), 126–149, written with Caullery.
Between 1900 and 1910 he wrote “Recherches sur l’Hemioniscus balani épicaride parasite des balanes,” in Bulletin scientifique de la France et de la Belgique, 34 (1901), 316–362, written with Caullery; “Recherches sur les orthonectides,” in Archives d’ anatomie microscopique, 4 (1901), 381–470, written with Caullery; “Les trypanosomes des poissons,” in Archiv fur Protistenkunde, 1 (1902), 475–498, written with Laveran; “Recherches sur les Fecampia, turbellariés rhabdocèles parasites internes des crustacés,” in Annales de la Faculté des sciences de Marseille, 13 (1903), 131–167, written with Caullery; “Contribution à l’étude des entéropneustes,” in Zoologisehe Jahrbuch Abteilung für Anatomie, 20 (1904), 227–256, written with Caullery; “Recherches sur les haplosporidies,” in Archives de zoologie expérimentale et générale, 4th ser., 4 (1905), 101–181, written with Caullery; and “Sur les propriétés préventives du sérum des animaux trypanosomiés. Races résistantes á ces sérums,” in Annales de l’Institut Pasteur, 23 (1909), 129–154, written with E. Brimont.
After 1910 he published “Sur deux monstrilides parasites d’annélides,” in Bulletin scientifique de la France et de la Belgique, 48 (1914), 15–29, written with Caullery; “Notes biologiques sur les mares à Lithothamnion de la Hague,” in Bulletin de la Société zoologique de France, 40 (1915), 160–161, 176–178, 198–200, written with Caullery; Xenocoeloma brumpti, copépode parasite de Polycirrus arenivorus,” in Bulletin biologique de la France et de la Belgique, 53 (1919), 161–233, written with Caullery; and "Ancyroniscus bonnieri, épicaride parasite d’un sphéromide (Dynamene bidentulata),” ibid., 44 (1920), 1–36, written with Caullery.
II. Secondary Literature. Obituaries include M. Caullery, in Presse médicale, no. 21 (12 Mar. 1938), 401–402; and in Bulletin biologique de la France et de la Belgique, 77 (1938); and G. Ramon, in Bulletin de l’Académie de médecine, 119 (1938), 241–247. Unsigned obituaries are in Bulletin de la Société de pathologie exotique, 31 (1938), 173–177; Bulletin de l’Institut Pasteur, 36 (1938), 177–179; Annales de l’Institut Pasteur, 60 (1938), 221–226; and Archives de l’Institut Pasteur, 16 (1938), 1–2.