1940: Biological Chemistry

In relation to biochemistry, the two fields in which most rapid progress was made during the year 1940 were (a) in the use of radioactive 'tracer' elements and (b) in the study of vitamins. Each of these two types of study was extended into many phases of the broader problem of gaining a better understanding of the chemical reactions that characterize living cells.

Biochemistry.

Animal Cell Utilization of Carbon Dioxide.

One of the most far reaching discoveries of the year was the finding (corroborated in different laboratories) that animal cells can maintain a rigid utilization of carbon dioxide gas, building it into their tissue constituents such as glycogen (animal starch) and certain organic acids. It has long been known that green plants can utilize carbon dioxide during photosynthesis to form starch, sugars, and other cellular ingredients. In animal cells, however, carbon dioxide has been looked upon as an end product, without thought of its re-use in cellular synthesis. The new evidence was obtained by the use of short-lived radioactive carbon, so that the experiments were of necessity very limited in time range. When larger quantities of the more suitable form of radioactive carbon (longer half-life) become available, investigations of a biochemical nature will be facilitated to an unprecedented degree.

Source of Energy for Photosynthesis.

The energy required for photosynthesis in green plants must come ultimately from sunlight, but during the past year two discoveries extended the recognition of relatively new factors that may be involved. Chlorella cells (a green, microscopic, unicellular plant) were found to continue reactions that constitute a part of the over-all photosynthesis through unexpected long periods of darkness. Under special circumstances, too, the cells could utilize hydrogen gas as a significant source of energy.

Formation of Animal and Plant Starch.

Cori's brilliant demonstration that glucose (blood sugar) forms an intermediate phosphate ester, glucose-1-phosphate, from which animal starch (glycogen) is formed directly in muscle and liver cells, has been extended in a general way to include the formation of starch in plants.

Plant Immunity.

An interesting phase of research relative to immunity was opened up by the finding that certain green plants and moulds could acquire immunity against different kinds of infectious (and virus) diseases, analogous to the long-recognized development of immunity against disease in animals.

Use of Radioactive 'Tracer' Elements.

The radioactive minerals, such as potassium, sodium and phosphate salts, have been used with notable success in following the course of salts through different channels of circulation in plants, and also in the basic study of cell permeability.

Copper.

Radioactive copper was found to be distributed rapidly into the tissues of anemic albino rats. There copper gave rise to the formation of active respiratory catalysts containing iron. Two of the major respiratory enzymes, cytochrone oxidase and catalase, are thus dependent upon the availability of copper as well as iron in such tissues as the bone marrow and liver; within 24 hours very low levels of activity are raised practically to normal by the feeding of minute amounts of copper.

Fluoride.

Increasing attention centered on the apparent function of fluoride as a factor of significance in relation to the development of good teeth. High fluoride intakes clearly produce mottled enamel, but there has been increasing evidence that intermediate levels may aid in the prevention of dental caries.

Vitamins.

The chemistry of the vitamins progressed rapidly along four major lines, (a) identification of new vitamins, (b) working out quantitative methods of chemical analysis that can be applied to tissue studies, (c) finding the chemical reactions by means of which the vitamins function in living cells, and (d) studying the significance of the vitamins in relation to human health.

Identification of New Vitamins.

Water-soluble forms of vitamin K were introduced widely, making the administration of the product simpler and obviating the parallel use of bile salts. Pantothenic acid, recognized first as a yeast stimulant by R. J. Williams, was found to be identical with the chicken anti-dermatitis factor and also to be one of the factors in the old vitamin B-complex that is essential for rats. Direct synthesis proved its constitution beyond doubt and provided an abundance of the pure compound for plant, animal, and clinical research.

Of similar interest was the finding by Wolley that inositol, recognized for many years as a yeast growth stimulant, or bios, was an essential factor in the nutrition of white mice. Apparently this new member of the vitamin family is not essential for rats, though very widespread in occurrence.

The anti-gray hair factor, required by rats and foxes, and once thought to be a single vitamin, was shown to be a multiple factor; at least some of the types of graying can be cured by riboflavin, vitamin B₆ or even certain minerals.

Commercial Production.

Among the outstanding accomplishments of the year was the production of pure riboflavin in commercial quantities at low cost by plant growth. The commercial production of vitamin B₁ and nicotinic acid by chemical synthesis has advanced rapidly to meet an expanding market. The low-cost availability of these three dominant members of the vitamin B-complex has added a great impetus to the movement to restore the vitamin content of wheat flour, so that a highly satisfactory grade of flour will be available with a content of the above three vitamins that is equal to that of whole wheat. Government officials, nutrition workers, the medical profession and the industrial millers have cooperated in making such a product available because of its evident contribution to public health. Realization of the extent of malnutrition in the United States and an intense effort to focus attention upon factors that would contribute to improved national health and efficiency have added force to the long over-due emphasis upon a bread of high nutritional quality.

Study of High Blood Pressure.

Very encouraging progress was made in the chemical study of substances that cause or alleviate high blood pressure. Proteins formed in the kidney tissue and circulating in the blood stream appear to comprise the primary disturbing factors. Restriction of the blood supply to the kidney, as shown earlier by Goldblatt, can cause the experimental type of high blood pressure, and evidence has accumulated rapidly to show the importance of the experimental animal technique in an approach to the clinical problem.

Chemotherapy.

The phenomenal success of synthetic sulfanilamide and sulfapyridine type compounds in the treatment of pneumonia and other diseases has led to very extensive studies of molecular structures that might provide even more effective agents in medical practice. Sulfathiazole (2-sulfanilylaminothiazole) was approved for general use by the medical profession. It was found to be especially effective in treating pneumococcic and staphylococcic infections and had less tendency to cause nausea. Two additional compounds of related structure appeared to be very promising: sulfadiazine (2-sulfanilamidopryimidine) and sulfaguanidine (sulfanilylguanidine). Because of its very low rate of absorption from the intestinal tract, the latter compound was viewed as especially promising for treatment of infections in the intestinal tract. The progress that has been made has been largely on an empirical basis, following analogies in structure rather than principles of a physiological nature. The results with the new tools of research, however, have greatly stimulated a renewal of interest in fundamental research in the field of chemotherapy. See also CHEMISTRY.

1939: Biological Chemistry

Progress during the year has been notable in each of the major fields of biochemical study: (1) photosynthesis, by which carbon is reintroduced into the biological cycle for both plants and animals; (2) the chemistry of plant growth, in a nutritional sense; (3) the mineral and organic requirements for animal nutrition; (4) basic cellular reactions by which foodstuffs are burned and energy is derived for life processes; and (5) the chemical aspects of fighting diseases.

Plant Chemistry.

Storage of Carbon Dioxide.

In the over-all economy of plants and animals, probably no chemical reaction is of more interest or fundamental importance than that of recovering carbon dioxide from the air and storing it in complex products such as sugars, proteins, fats and their related constituents of living cells. A primary clue of the greatest interest was provided by the use of radioactive carbon at the University of California, where it was found that the apparent first entry of carbon dioxide into a fixed, complex substance in the cell was to form the acidic carboxyl (-COOH) group in an acid of fairly high molecular weight. There is some evidence that one of the primary steps in photosynthesis is a reversal of the reaction by which carbon dioxide is known to be split out of the cellular products of oxidation. Vitamin B₁ plays the role of a catalyst for the reaction by which carbon dioxide is formed in both plants and animals, thus linking one of the first-discovered vitamins with both respiration and photosynthesis. Copper, vitamin C and the carotenoid pigments are also highly concentrated with chlorophyll in the granules where photosynthesis takes place. The photosynthetic reactions are extremely sensitive to the effect of inhibitors or poisoning reagents that affect cellular respiration at higher concentrations, thus further linking together the general course of the two major types of reaction in plant cells.

Plant Nutrients and Stimulants: Vitamins.

In their study of mineral requirements for plant growth, Arnon and Stout observed an increased rate of growth when molybdenum salts were supplied to tomato plants in a concentration of 1 part in 100 million, thus adding a new element to the steadily growing list of 'essential' nutrients. Three laboratories obtained further evidence of the essential nature of silicon for plant growth; and additional evidence of the importance of boron for the growth and fruiting of cotton plants was found at the Georgia Agricultural Experiment Station. At Columbia University, extreme variations in different plants were found with respect to calcium and magnesium requirements and antagonisms, and also in relation to the effect of selenium. The latter element is toxic toward many plants, but evidence was obtained of a positive effect upon growth in some plants. Lundegardh observed a marked stimulating effect of manganese salts upon the respiratory activity of wheat root cells, and suggested that in some plants, the role of manganese is similar to the role of iron in others.

The importance of organic nutrients for plant growth has become recognized more clearly, and fascinating insights have been provided to explain many peculiarities of plant behavior — particularly the effects of one kind of plant upon another, and the interrelationships of plants and animals. Many of the phenomena related to symbiosis, parasitism and soil fertility are clearly dependent upon the supplying of vitamin-like compounds, or bioses, from one plant to another or from animals to plants. In the past, the emphasis has generally been in one direction only — plants providing vitamins for animals. The isolated, pure vitamins of the B-complex have been particularly useful in studying plant growth requirements. The growth responses of different lower plant forms (bacteria, yeasts and molds) have been found to be so specific in a number of cases that they provide a basis for quantitatively measuring the vitamin content of foods and extracts from animal tissues. Such quantitative relationships have been demonstrated for thiamine (B₁), riboflavine (B₂), nicotinic acid amide (G), and the filtrate factor (related to pantothenic acid). Vitamin C also acts as a growth-promoting hormone. One of the most striking relationships of this kind was brought out by Moewus (University of Erlangen), who found that some of the green algae were sensitive, as measured by their capacity for locomotion, to a concentration of 1 part of crocin in 250 trillion parts of nutrient solution. Crocin is a glycoside of crocetin, a fatty acid closely related in structure to vitamin A, phytol, and the carotenoid pigments. Vitamin B₁ has come into common usage almost suddenly as a growth stimulant in household flower culture. Cystcine, a common unit in proteins, also came into wider recognition for its growth-promoting activity in plants.

Wound Hormone; Fatty Acids.

The plant wound hormone, traumatic acid, was isolated and identified as 1-decene-1, 10-dicarboxylic acid by English, Bonner and Haagensmit during the year. Injury to plant tissues stimulates formation and activity of the hormone in the processes of cell proliferation and wound-healing. Another development of special interest related to fatty acids in plants was the extension of the chaulmoogric acid series to include four new members, by Cole and Cardoso. The two higher homologues, known earlier, are perhaps the most effective agents available for combatting leprosy.

Animal Nutrition.

Zinc.

The animal requirement for minute amounts of mineral elements has continued to be an active and fruitful field of investigation. No new elements were added to the 'essential' list during the year, but a clearer insight was gained concerning the function of the less common elements. One of the striking discoveries was the finding by Keilin and Mann that a zinc-protein compound could be isolated from beef red blood corpuscles (0.31 to 0.34 per cent Zn). The zinc compound proved to be the catalyst that controls the conversion of carbonic acid to carbon dioxide and water, hence called carbonic anhydrase. Zinc thus controls one of the major respiratory functions in the animal body, making it possible for carbon dioxide to escape from the blood stream as it courses through the lung capillaries.

Copper.

The role of copper in the animal body was further clarified by Schultze, who found that the copper intake constituted a limiting factor in the rat's capacity to make one of the major oxidative catalysts, cytochrome oxidase. The chemical nature of cytochrome oxidase, however, is not fully known; hence the role of copper in this case may be analogous to its role in making possible the synthesis of hemoglobin and other iron compounds.

Cobalt.

Elvehjem and associates have demonstrated the essential role of another metal, cobalt, for hemoglobin synthesis in dogs. Previous observations under natural grazing conditions had correlated cobalt deficiency with anemia in cattle and sheep, but an experimental deficiency had not been accomplished. The new finding makes it possible to study the role of cobalt under carefully controlled laboratory conditions.

Manganese has been further studied by Norris in relation to perosis (slip, or detachment of tendons) in birds. A low intake of the metal in chick diets also resulted in low egg hatchability and high chick mortality.

Selenium.

No evidence has appeared to indicate that selenium has a nutritive value for animals, but additional evidence concerning its toxicity was reported by Twomey and associates, who observed fairly extensive selenium poisoning of ducks under natural feeding conditions.

Fluorides.

Although most of the biochemical studies on fluorides have dealt with their toxicity, evidence now indicates that a marginal intake of fluoride affords a certain degree of protection against dental caries. Cox and associates have succeeded in producing experimental mottled enamel in rats, and have further demonstrated a protective effect against dental caries in rats under carefully controlled experimental conditions. McKay, Dean, and others have observed from clinical survey data a positive correlation between mottled enamel areas and a low incidence of dental caries. Armstrong and Hodge have contributed further observations that indicate a beneficial effect of fluorides upon tooth structure and resistance to caries. The normal presence of fluorides in bones and teeth has been recognized over a long period.

Vitamin B-complex.

Rapid progress has been made in the study of the vitamin B-complex, both in relation to the number of factors that are included in the complex, and in regard to their structure and function. Elvehjem regards the evidence to be satisfactory for the existence of at least 10 separate entities in the 'B-complex.' Of these thiamine (B₁), riboflavine (B₂), nicotinic acid (G) and B₆ have been identified as pure compounds and synthesized on a commercial scale. Beta-alanine is known to be an essential part of the 'filtrate factor' and pantothenic acid (possibly identical). The other factors are essential for either rats or chicks or both. The existence of an anti-gray hair factor has been verified in a number of laboratories, but there has been no evidence that gray hair in people is related to such a nutritional deficiency. All of the above four isolated factors have been shown to be essential for human nutrition, as shown particularly by Spies, Sebrell and associates through their feeding of pure vitamin supplements to pellagrins.

Vitamin K.

Vitamin K has been isolated and synthesized in a number of laboratories, largely through the work of Dam, Almquist, Daisy, Ansbacher, Anderson, Fieser and associates. A whole series of 2, 3-substituted anthraquinones, natural and purely synthetic, can serve as vitamin K in the body. Clinical usage of vitamin K (both natural and synthetic) to promote blood clotting has been very widely adopted. Aside from the early discovery of the existence of the vitamin by Dam, nearly all of the later progress was accomplished in American laboratories.

Vitamin C.

Studies of the functional role of vitamin C have led to confirming its close relation to tooth development, resistance against bacterial toxins, and to complement activity in the blood stream. The rate of synthesis in rats was brought under experimental control to a great extent by the work of Longenecker and associates, using pure compounds to effect an increased rate of synthesis and excretion. The vitamin is also an important factor in regulating the metabolism of aromatic amino acids, as shown by Levine and associates. Peugnet observed a functional rôle, in association with copper, in regulating the heart (frog).

Nutrition and Teeth.

The predominant importance of good nutrition for the development of sound teeth and protection against the incidence of dental caries was brought out in striking fashion by extensive surveys in England, particularly those reported by Read and Miller and their associates. According to their findings dental hygiene, as ordinarily understood, has little to do with protection against tooth decay, at least up to the age of 14 years.

Physiological and Clinical Chemistry.

The success of Cori and associates in demonstrating the synthesis of glycogen from hexosephosphate in vitro, by means of an enzyme extracted from muscle, was a finding of great fundamental significance. A key was thus provided to one of the most important physiological reactions — the synthesis and hydrolysis of muscle glycogen, on which most of the mechanical and chemical energy of the body depends.

Micro-methods of blood and tissue analysis, as extended during the year by Borsook and associates and others, opened up valuable techniques for the study of tissue changes. Fairly comprehensive analyses for intermediate metabolites can thus be made with samples as small as 0.1 to 0.2 ml. of blood. Of similar widespread importance are the rapidly developing micro methods for vitamin and mineral analysis, by which the state of nutrition of a person or animal can be determined with a degree of certainty that greatly enhances the possibility of detecting border-land types of malnutrition — a field of diagnosis that should greatly advance public health work.

The use of stable and radioactive isotopic elements in biological 'tracer' work has been adopted with great rapidity. Radioactive iron, phosphorus, sulfur, sodium and potassium have been used very widely, and the use of heavy hydrogen (deuterium), heavy nitrogen and heavy carbon has been extended steadily.

Considerable success has been achieved in the separation of compounds from kidney tissue that can be used for the study and perhaps the control of high blood pressure.

The preparation and use of sulfapyridine-type compounds for combatting infections has continued rapidly, with increasing effectiveness in clinical practice. Sulfathiazole has been especially promising as a new product. Approximately 800 such compounds have already been studied.

Enzymes and Respiratory Carriers.

The problem of isolating and identifying enzymes and respiratory catalysts has been studied extensively and with continued success. Papain, a protein-splitting enzyme was isolated from plant sources by Balls and Linneweaver. Chymotrypsin, a protein-digesting enzyme isolated earlier by Northrup and associates from the pancreas was converted into two new crystalline enzymes by Kunitz. The latter also isolated a ribonuclease from beef pancreas. Sumner, who was the first investigator to isolate successfully a crystalline enzyme (urease), recently succeeded in isolating another important enzyme, catalase.

The respiratory-carrier enzymes studied most effectively during the year have been those containing riboflavins linked to specific proteins, active carriers in the first steps of burning foodstuffs within the cells. Considerable progress was also made in identifying cytochrome oxidase and the cytochromes — agents that act most directly upon molecular oxygen as it enters into the chain of reactions that ultimately result in the formation of water and carbon dioxide, plus the energy for life processes. See HORTICULTURE.

1938: Biological Chemistry

Fields of Research.

Chemistry in relation to biology, or biochemistry, overlaps frequently other fields of scientific study, such as agriculture, medicine, physiology, and bacteriology. The major fields of research in biological chemistry can be satisfactorily viewed, however, in terms of the primary purposes involved: (a) to gain a clearer insight into the structural nature and composition of living cells; (b) to follow the chemical changes that characterize the life processes of each type of tissue; and (c) to study in a fundamental manner the problems of growth, nutrition, health and disease. Although progress has continued steadily in each of these three fields for a number of years, only very incomplete concepts are yet available concerning the composition and function of the simplest cells.

Structure and Composition.

Proteins, which constitute the dominant part of the active cell mass, have been studied extensively and continuously in many laboratories. The most important recent advances in unraveling their make-up have been in relation to their particle size, their structure when oriented in films and crystals, and the exact mode of linkage of their structural units, the amino acids. Bergmann's work has been of special interest in establishing the regularity of the sequence of amino acids in the long, chain-like structure containing approximately 288 individual unit parts. The larger protein particles appear to be built up as multiples of the 288 unit particles, in agreement with the earlier findings of Svedberg that protein generally had molecular weights of 34,500 or multiples of that number.

The repeated isolation and identification of huge protein molecules, that occur as filterable viruses and bacteriophages, by Stanley, Northrop, and Wyckoff have led to a new phase of protein studies. The molecular weights of crystalline virus proteins have been reported as approximately 20,000,000, and Wyckoff has reported values as high as 300,000,000 for the molecular weight of bacteriophages. The particles appear to possess autocatalytic power, producing increasing amounts of like protein material from the cellular constituents of bacteria or host tissue, as in tobacco-mosaic. Particles of the nature of viruses and bacteriophages represent the nearest approach to bridging the gap between living and non-living material. The possibility remains that bacteriophages represent true portions of living matter rather than pure crystalline proteins in the usual sense of referring to a pure compound. The presence of nucleic acid in the bacteriophages provides preliminary evidence of the presence of nuclear portions of cell structure.

The detailed chemical structures of starches, cellulose, and the simpler sugars have been established much more clearly than the nature of the proteins. Hence, recent progress in the study of the carbohydrates has been less striking, and characterized by gradual progress rather than by major advances.

The study of oils and fats has progressed steadily in regard to (a) the nature of the non-soap-forming fraction, and (b) the distribution of fatty acids in accordance with biological classification. Searching for vitamins and hormones in the unsaponifiable matter of fatty materials has led to the realization that hydrocarbons, alcohols, ethers, esters, ketones, and a great variety of physiologically important types of compounds are normally present in nearly all natural fats. In only a few cases has it been possible to assign functional activity to the non-fatty-acid portion of fats, but the recent trends of investigation point toward an increasing recognition of the importance of such compounds in both plant and animal physiology. The fact that compounds in this class of materials (unsaponifiable matter) furnish vitamins A, D, E, and K, the cortical hormones and the sex hormones, may serve to illustrate their importance.

The problem of molecular structure in relation to the fatty acids in oils and fats has been studied chiefly by Hilditch and associates, who have been able to correlate a number of chemical characteristics with biological classifications in both animals and plants.

An accomplishment of unusual interest was the preparation of optically active fats by H. O. L. Fischer and associates. Esters of glycerol with fatty acids and phosphoric acid were prepared from the optically active glyceric aldehydes, which were, in turn, prepared from d- and l- forms of a common sugar, mannose.

The catalysts (enzymes) which control the rate of nearly all chemical reactions in living cells are now known to be essentially proteins. The pioneering work of American investigators in proving the protein nature of enzymes, especially the work of Sumner, Sherman, and Northrop, long in disagreement with the German research school headed by Willstaetter, has been fully confirmed. Many of the enzymes have been obtained in pure, crystalline form, and in every case they have proved to be proteins. The digestive enzymes and a number of others have not shown any evidence of the protein being linked to a special, catalytically-active group; but the enzymes that control the combustion processes in the body have been found, in a number of cases, to have a special (prosthetic) group attached to a native protein. Both parts of the molecule are essential to its normal rôle. Metallic elements such as copper and iron, and organic groups such as the vitamins have been identified as essential parts of enzymes. The native catalysts can be broken apart and again synthesized without loss in their catalytic activity or any apparent change in their properties. Copper is found in at least two such protein compounds in plants, and occurs in still other protein combinations in animals. More and more it becomes apparent that the remarkable effects of minute traces of many of the elements, the hormones, and the vitamins in the animal body, are due to their rôle as catalysts after being linked to specific proteins.

Although a knowledge of the nature of enzymes is basic to an understanding of even the simpler changes in all living cells, relatively few direct applications have been found for them in agriculture or medicine. Recent work has made use of the characteristics of one of the enzymes in milk, to provide the basis for a valuable and practical test for adequate pasteurization of milk. The heat treatment of milk that has proved to be adequate for making it safe from transmission of disease is also just sufficient to destroy the enzyme in milk that acts upon phosphate esters (phosphatase). Both low-temperature (142° F.) and high-temperature (160° F.) pasteurization of milk destroy the enzyme to a degree that makes the test of practical value for detecting underpasteurization.

Chemical Changes within the Body.

The use of 'tracer' elements to 'tag' foodstuffs, and thus to provide a means of following their course within the various parts of the body, has proved to be a very valuable technique. The work of Schoenheimer, Krogh, and others, using heavy hydrogen (deuterium) attached to fatty acids, furnished considerable insight into the changes that the fats undergo in the animal body. The study of nitrogen (and indirectly protein) metabolism has been undertaken in a similar manner by Schoenheimer and others using heavy nitrogen. Although the quantities of the heavy forms (isotopes) of the elements can be determined very accurately by analysis, their chemical reactions are essentially the same as the common forms of the elements, thus providing a means of tracing the course of a given fat or protein through successive stages of alteration within the different organs and tissues of the body.

More recently radioactive phosphorus has been used by Hevesy and Artom to study many phases of intermediate changes in fats and phosphates in biological processes. Lawrence and associates at the University of California have also launched a program of studies with radioactive elements in plant and animal cells. It is interesting to note how quickly the research tools of the physicists and physical chemists have been adapted to the study of physiological problems by those working in biochemistry.

Vitamins.

The general term 'vitamins,' to represent organic (carbon) compounds that are required in minute amounts in the food supply of animals, is still useful in both technical and lay literature. The use of a letter (A, B, C, or other) to represent each different vitamin has become less necessary, however, for several reasons. The number of such factors covered formerly by a single letter has made the use of letters often confusing and awkward. The former vitamin B₂, for example, included many different compounds with entirely independent functions and properties. The extensions of subscripts to B₃, B₄, B₅, B₆, etc., and the parallel introduction of additional letters, G, H, etc., to cover the same series of newly-identified vitamins led to considerable confusion. In addition, the work of Bills, Hicks, and others has shown that ten or more different compounds can all serve independently as 'vitamin D' in the animal body. The response, in terms of protective dosage, varies for the different forms of 'vitamin D,' depending upon whether the rat's, chicken's, or human's response is measured. In a similar sense, the vitamin A requirement can be provided for by feeding any one of six or more different compounds that are closely related in molecular structure. Hence as each vitamin-like substance becomes clearly identified chemically and physiologically, there is a great gain in clarity of expression when specific chemical names are used for each particular substance under discussion. In accordance with this trend toward chemical nomenclature, vitamin B₁ is called thiamin; one of the fractions from the old B₂ is riboflavin; and another (G) is nicotinic acid; and vitamin C is generally called ascorbic acid.

Recent progress in the study of vitamin A has been of special significance in relation to its formation of a series of colored protein compounds, visual purple, visual yellow, etc., in the retinal rods of the eye. The compounds are sensitive to light, undergoing a series of chemical changes that constitute an important part of the functioning of the eye. Attempts to test the rate of sight-recovery after exposure to a bright light for a clinical indication of the relative degrees of vitamin A deficiency have met with varied degrees of success. Some investigators have felt that there was a good correlation between the recorded time period of sight readjustment and state of nutrition, but others have observed very poor correlation between the test results and the apparent vitamin A intake. In addition to the vitamin A compounds observed in eye tissue, Hicks has brought out further evidence, by high-vacuum distillations, that vitamin A exists in fish-liver oils in a number of different ester-type combinations with fatty acids. High-vacuum distillations from fish-liver oils also demonstrated the occurrence there of a series of natural compounds having the common property of serving as vitamin D in the animal body.

Vitamin E, the third fat-soluble vitamin to be identified, has been synthesized recently, in the course of proving its exact molecular structure. There is still no generally accepted evidence of its value in clinical practice, although it is clearly essential for normal reproduction and protection from muscular dystrophy in rats. It also has the capacity to serve as an antioxidant or anti-rancidity agent in vegetable oils.

The newest fat-soluble vitamin is K, first identified as an anti-hemorrhagic factor for chicks. It is widely distributed in green leafy foods and may be found in animal fats. Cod-liver oil is deficient in the factor, and most cereals are deficient. Even though it has not been possible to demonstrate vitamin K deficiencies in humans or small experimental animals such as rats and guinea pigs, clinical usage of the vitamin has been reported for the purpose of promoting blood clotting. Delayed clotting time due to obstructive jaundice appears to respond favorably to vitamin K therapy, thus making the apparently non-essential vitamin a useful tool in surgery. Isolation of the crystalline vitamin has been reported, but its molecular structure has not been established.

The original vitamin B group has been extended to include at least five and probably eight or more factors. Of these, the molecular structures of thiamin (B₁), riboflavin (B₂), and nicotinic acid (G or B₂) have been clearly demonstrated, and syntheses on a commercial scale have been developed. During the past year vitamin B₆ was isolated as a pure compound, but its complete structure was not established.

The function of vitamin B₆ was shown to be related to the utilization fats in the animal body and to the protection of rats against a peculiar type of skin lesion. The latter was most marked about the paws, eyes, and mouth.

Late in 1937, Elvehjem and associates at the University of Wisconsin gave a preliminary report of the isolation and identification of nicotinic acid and its amide as the anti-black tongue factor for dogs. They also pointed out the probability that the same compound would cure human pellagra. Within a very short time Spies and others at the University of Cincinnati reported the successful cure of clinical pellagra, probably America's most damaging deficiency disease, by the use of nicotinic acid. This finding provided a beautiful illustration of the way in which a research finding with small laboratory animals under carefully controlled conditions may be utilized for the improvement of human health on a large scale. Detailed reports of the work at the University of Wisconsin and in a number of medical centers appeared during 1938. Nicotinic acid (as its amide derivative) had been identified earlier as a growth stimulant for some of the lower forms of plant life and as a catalytic agent in the burning of foodstuffs in the animal body. The vitamin apparently combines with phosphoric acid and specific proteins in living plant and animal cells to form one of the chief catalysts or 'carrier agents' concerned with combustion types of reaction. The primary action of the vitamin appears to be in removing two hydrogen atoms at a time from such food stuffs as sugars, and transferring them to other systems that finally carry them to oxygen breathed in from the air.

Vitamin B₁ is concerned primarily with splitting off carbon dioxide from foods being burned in the body. The Wisconsin group showed during the past year that the nerve degeneration, or polyneuritis (clinical beriberi) that is usually associated with a deficiency of vitamin B₁, is in reality a side effect, due essentially to other factors than a simple deficiency of B₁. Alcoholic polyneuritis, characterized by a deficiency of vitamin B₁, was shown to be fairly common in the United States and European countries. Careful studies with plants during the past year brought out a number of interesting facts regarding the growth stimulating effects of the vitamin and the variation in capacity of different plants for synthesizing the vitamin from simpler materials. Bonner and Robbins have been particularly active in studying the rôle of the water-soluble vitamins in plants.

Riboflavin, often referred to as vitamin B₂ in the older literature, has been shown to serve as another of the major 'carrier agents' in the combustion reactions within animal and plant cells. Like nicotinic acid and thiamin, it combines with phosphoric acid and specific proteins to serve as a catalyst.

Vitamin C synthesis can be accomplished by practically all plants and animals other than man, monkeys, and guinea pigs. The rôle of the vitamin in a chemical sense has not been established clearly. Work in the author's laboratory has shown that the vitamin probably does not function as a major 'carrier agent' in a manner similar to the rôle of the above B-complex factors. An entirely new relationship of the vitamin to the metabolism of volatile fatty substances in rats was shown during the year. In another laboratory its function as a plant growth stimulant was clearly demonstrated.

Chemotherapy.

Clinical success with the use of sulfanilamide-type compounds in combating such infections as pneumonia, streptococcic sore throat, gonorrhea, and streptococcic meningitis has stimulated an intensive extension of the work of chemists in the search for more effective compounds with less risk of injury in the course of treatment. Of the new types of compounds related to sulfanilamide, sulfapyridine has given the greatest promise, particularly in the treatment of pneumonia.

An entirely independent research program by Cretcher and associates at the Mellon Institute, in collaboration with Dr. Maclachlan and associates for the clinical work, has developed a promising antipneumococcic agent that is derived from the cinchona alkaloids (a series that is closely related to quinine). Their product is less toxic than the sulfanilamide or sulfapyridine types of compounds and is highly protective.