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Mendel, Lafayette Benedict


(b. Delhi, New York, 5 February 1872; d. New Haven, Connecticut, 9 December 1935)

physiological chemistry.

Lafayette Benedict Mendel was the elder of two sons of Benedict Mendel, a merchant in Delhi, New York, and Pauline Ullman. Both parents migrated to the United States from Germany. Mendel prepared for Yale College in the local schools and in 1887, at the age of fifteen, obtained a New York State scholarship by competitive examination. At Yale he studied mainly the classics, economics, and the humanities, but on graduation in 1891 was awarded a fellowship that enabled him to enter the graduate course in physiological chemistry under Russell H. Chittenden of the Sheffield Scientific School

Although poorly prepared in chemistry and physics and without experience in laboratory work, Mendel completed the requirements for the Ph.D. in two years with a thesis on the proteolysis of the crystalline hempseed protein edestin. This investigation was of no lasting significance, but the work aroused his interest in protein chemistry, and especially in the properties of the proteins of plant seeds. This was to have great influence upon his later career.

Mendel joined the teaching staff of the Sheffield Laboratory of Physiological Chemistry in the fall of 1893. He took a year’s leave of absence in 1895 and went to Germany, where he studied physiology at Breslau with R. Heidenhain and chemistry at Freiburg im Breisgau with E. Baumann. He quickly established his position in Heidenhain’s laboratory by demonstrating the preparation of crystalline edestin from hempseed, something that the professor had never seen before.

In 1897 Mendel was appointed assistant professor and in 1903 full professor of physiological chemistry in the Sheffield Scientific School. In 1921 he was made Sterling professor of physiological chemistry at Yale University, one of the first of these distinguished appointments, with membership in the faculties of the graduate and medical schools. Mendel was a most effective teacher. His lectures were clear and forceful, scholarly and stimulating. In his seminars, where weekly discussions of current advances in biochemistry were held, he taught his students to teach, always insisting on dignity in presentation, good English style, and accuracy of statement, qualities that he illustrated in his own discussions of the matter at hand. He communicated his own enthusiasm to his students and took a close personal interest in all of them, winning their confidence and respect and caring for their interests long after they had left Yale for positions elsewhere.

Mendel’s early scientific work illustrates the influence of his teachers: from Chittenden the interest in proteins, from Heidenhain that in experimental physiology, and from Baumann the biochemistry of such compounds as creatine, choline, taurine, the purines, and especially the iodine-containing substances of the thyroid gland. With the collaboration of colleagues on the faculty and of a steadily increasing number of graduate students, papers were published on such subjects as the nitrogen metabolism of the cat, the formation of uric acid, the paths of excretion of a number of inorganic ions, the metabolism of iodine, of allantoin, of kynurenic acid, and of several pyrimidines and purines. His interest in nutrition was aroused early. The first paper on the subject was published in 1898 and dealt with the nutritive value of various edible fungi. As early as 1906 he began his studies of growth, one or another aspect of which was dealt with in about seventy subsequent papers.

Mendel is remembered chiefly as coauthor, with Thomas B. Osborne of the Connecticut Agricultural Experiment Station in New Haven, of more than one hundred papers on the subject of nutrition. This collaboration began in 1905 with a study of the proteins of the castor bean, especially the highly toxic albumin ricin. Osborne, with his assistant Isaac F. Harris, prepared the proteins, and Mendel did the physiological tests. Their most active preparation of ricin was fatal to rabbits at a dose of two one-thousandths of a milligram per kilogram, and they thoroughly established the protein nature of this extraordinary poison, then a matter of debate.

The collaboration with Osborne on the nutritive effect of proteins began in 1909. Osborne had become an internationally known authority on the preparation and properties of the proteins of plant seeds and upon their analysis by the then current methods. The question had arisen whether substances of such widely varied amino acid composition were equally effective for the protein nutrition of animals, a matter upon which divergent opinions were held, and he invited Mendel to join him in an investigation of the subject. Together they devised improved experimental methods for feeding white rats, including accurate measurements of food intake, and adopted the general principle that in a successful experiment the food must maintain the weight of the rat for a substantial fraction of its life span. Rats had been used previously for studies of nutrition by a number of European investigators, such as V. Henriques in Copenhagen and W. Falta in Basel. They had also been used in this country by Henry H. Donaldson of the Wistar Institute in Philadelphia and by E. V. McCollum of the University of Wisconsin.

Aided by annual grants from the Carnegie Institution of Washington, they soon established that the diet must contain adequate amounts of lysine and tryptophan, supplied either as such or combined in the protein of the diet. This was the first convincing proof that certain amino acids are essential components of the diet and cannot be synthesized by the animal organism. Despite every care nutritive failure ultimately supervened. A preparation obtained by evaporating milk serum to dryness, the so-called protein-free milk, greatly postponed such failures when included in the food; but, even so, sudden and dramatic losses of weight and ultimately death occurred. The animals could be saved by furnishing a diet which contained dried whole milk, but not by one containing dried skim milk. This dillerence led to an examination of the effect of supplying butter for a part of the lard in the food. The result was a demonstration that butter contains an organic substance, obviously present only in trace amounts, which is essential in the nutrition of the rat. This finding was the discovery of vitamin A. Unfortunately for Osborne and Mendel, McCollum at the University of Wisconsin had made a similar observation and had submitted his results for publication a few weeks before Osborne and Mendel’s paper was received. McCollum is thus regarded in the history of biochemistry as the discoverer of vitamin A.

Nevertheless, the independent and almost simultaneous publication of so important a conclusion from two laboratories greatly strengthened the position of both groups of investigators, and the doctrine that an adequate diet must supply trace amounts of hitherto unrecognized organic substances was at once widely accepted. It led within a few years to a complete revolution in the science of nutrition. The “protein-free milk” was recognized to contain a second such essential, which was soon designated water-soluble vitamin B and Osborne and Mendel for some ten years devoted much study to the distribution of these essential substances in natural food products and to the elucidation of the complexities of the water-soluble vitamins.

Once they had established that diets of purified food materials could be compounded upon which rats would grow well and live indefinitely, Osborne and Mendel carried out many studies of growth. From the beginning of the period of collaboration with Osborne, Mendel’s bibliography contains 289 titles. Of these, 24 percent contain the word “growth.” Perhaps the most striking result was the demonstration that the growth of a young animal could be indefinitely suppressed and then resumed by manipulation of the diet with respect to the supply of lysine. Growth could occur at any age.

Notwithstanding the time and effort expended upon the collaboration with Osborne, Mendel also directed the activities of many graduate students. Especial attention was given to the chemistry and metabolism of fats and to the regulation of blood volume by the supply of salts. He was frequently invited to give lectures and also served as a consultant not only to his medical colleagues but also to the food industry, Withal, he was a professor who is remembered by his students with deep affection and respect. Always approachable and kindly, ever ready with suggestions for the solution of practical problems or with helpful reference to the literature of his subject, of which he was a complete master, his influence upon science at Yale and especially upon the medical applications of nutrition was great. Largely through his own efforts nutrition was transformed during his lifetime from empiricism to a clearly recognized branch of biochemistry founded upon scientific principles. When it is realized that the modern poultry and meat industries rely entirely upon the proper supply to the animals of vitamins and of proteins of correct and adequate amino acid composition, the benefit to practical agriculture of Mendel’s work is almost incalculable.


I. Original Works. Mendel’s bibliography in Russell H. Chittenden’s memoir, Biographical Memoirs of the National Academy of Sciences, XVIII (1937), lists titles of 326 papers, nearly all being records of scientific research published between 1894 and 1935. It is incomplete since Mendel, who prepared it, did not include numerous editorials in the Journal of the American Medical Association and many book reviews and similar less important writings. Of these papers 111 were written in collaboration with Thomas B. Osborne of the Connecticut Agricultural Experiment Station and record joint experiments made between 1910 and 1928 in Osborne’s laboratory with financial support by the Carnegie Institution of Washington and the Connecticut Station. Most of them were published in the Journal of Biological Chemistry After Osborne’s retirement in 1928 and death in 1929, the work at the station was continued until Mendel’s death in 1935, some fifteen papers being published with several junior collaborators, During this same period Mendel published ninety-seven papers in collaboration with graduate students or colleagues on the Yale faculty, and forty-one, mainly reviews of various aspects of nutrition, of which he was sole author. Mendel gave lectures subsequently published before the Harvey Society of New York in 1906 and 1914 and also gave the Herter Lectures at University and Bellevue Hospital Medical College in New York in 1914. In 1923 he gave the Hitchcock Lectures at the University of California and in 1930 was Cutler Lecturer at the Harvard Medical School.

Publications in book form include Feeding Experiments with Isolated Food-substances, 2 pts., Carnegie Institution of Washington Publication No. 156 (1911); Changes in the Food Supply and their Relation to Sutrition (New Haven, 1916); and Natrition the chemislry of Life (New Haven. 1923).

II. Secondary Literature. In addition to the memoir by chittenden mentioned above, there is a tribute by A. H. Smiill. in Journal of Nutrition, 60 (1956), 3.

H. B. Vickery

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"Mendel, Lafayette Benedict." Complete Dictionary of Scientific Biography. . 14 Dec. 2017 <>.

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Mendel, Lafayette Benedict

Mendel, Lafayette Benedict (1872–1935) American chemist; jointly with Osborne pioneered studies of protein quality; discovered vitamin A (1913).

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"Mendel, Lafayette Benedict." A Dictionary of Food and Nutrition. . 14 Dec. 2017 <>.

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"Mendel, Lafayette Benedict." A Dictionary of Food and Nutrition. . Retrieved December 14, 2017 from