Popular Science Monthly/Volume 83/November 1913/The History of Dietetics
|THE HISTORY OF DIETETICS|
THE manifold diversities in diet, the articles employed as food, the manner of preparing food, customs of eating, etc., among different peoples and at different times have been the outcome of fortuitous evolution, unguided and uninfluenced by definite physiologic principles. An account of the development of such dietary practises would present much of interest and would be included in a complete history of dietetics; but it is far too large a subject to be considered here, and the present paper will be limited to a brief presentation of the development of the various lines of knowledge constituting the scientific basis of dietetics, as it exists to-day.
Inquiring and speculative minds in all ages have endeavored to trace out the principles and laws governing diet. Prior to the modern scientific era, that is, during the entire ancient and middle ages, there was very little foundation of real knowledge on which a true science of dietetics could be based. Only the crudest objective characteristics of foodstuffs could be appreciated, such as the division of animal and vegetable, liquid and solid, etc. Notwithstanding the want of any adequate basis, from the time of Hippocrates a large proportion of medical literature was devoted to the subject of dietetics, and a multitude of treatises on food were presented characterized by chimerical speculation and fine-spun theorizing. Mythical properties and dangers were ascribed to different foodstuffs; rules were laid down in minute detail as to the use or prohibition of various foods in different morbid conditions which were without rational warrant; dietetic theories and systems were propounded which in the light of modern knowledge are seen to have been grotesque; and the authorities expounded their doctrines with an emphasis and dogmatism paralleled only by their real ignorance of the subject. Of all the mass of dietetic doctrine presented in the ancient and medieval eras of medical thought, there was very little of abiding verity or value that contributed to our present rational knowledge of the subject. On the contrary, the professional mind was thoroughly indoctrinated with erroneous ideas which retarded the acceptance of correct conceptions and have not even yet been eradicated.
The science of dietetics is a composite subject, uniting a number of rather independent branches of knowledge, such as the chemistry of food, the processes of digestion, the physiology of metabolism, etc., the development of which may be separately considered. The beginnings of our scientific knowledge of these subjects may be traced back to the seventeenth century, soon after the discovery of the circulation of the blood by William Harvey (1578-1667), announced in 1628, opened the way to the development of scientific physiology. No great progress, however, was made for nearly two centuries, and the main foundations of our knowledge of these subjects were laid down in the second quarter of the nineteenth century.
The development of our knowledge of the physiology of digestion will be first considered.
A knowledge of the mechanism of glandular secretion in general is prerequisite to an understanding of the origin of the digestive fluids. No adequate conception of the structure and function of glands was possible prior to the discovery of the circulation and the use of the microscope. When these conditions were fulfilled the physiology' of glandular secretion was quickly worked out. At first, for instance, it was not even known that, except for the liver and kidneys, the glands possessed ducts. The main steps in the evolution of our knowledge of glandular action were about as follows:
In 1643 the duct of the pancreas was first described by Georg Wirsung, a Bavarian (died 1643), although his pupil Maurice Hoffmann contested the honor of its discovery as his own. In 1654 Francis Glisson, an Englishman (1597-1677), published an important work on the liver, in which he touched upon the mechanism of the secretion of the bile. In 1656 Thomas Wharton, an Englishman (1610-1673), published an account of the duct of the submaxillary gland. In 1662 Lorenzo Bellini, of Florence (1643-1704), at the early age of 19 years, described certain portions of the uriniferous tubules of the kidney. In 1663 also Nicolas Stensen, or Steno, a Dane (1638-1686), described the ducts of the parotid and other glands. The names of these observers have ever since been attached to the structures which they discovered.
About this time Franciscus Sylvius, Stensen's instructor at Leyden, drew a general distinction between conglomerate glands, possessing secretory ducts, such as ordinary secreting glands, and conglobate glands, such as the lymphatic glands. Stensen, from his researches on the salivary and other glands, came close to an adequate conception of the process of glandular secretion; but as, like the other observers just mentioned, he did not employ the microscope, he was unable to work out the full details of the subject. It remained for Marcello Malpighi (1628-1694), of Bologna, a pioneer microscopist and one of the first and greatest of histologists, in 1666 to lay down finally the essential features of the minute structure and mechanism of the main glandular organs as they are accepted at the present time.
The wikt:lactealslacteals were discovered in 1622 (published 1627) by Gaspare Aselli (1581-1626), professor at Pavia, who recognized that they conveyed the chyle away from the intestine, but regarded them as emptying into the liver, then thought to be the organ in which the food materials were converted into blood. The discovery of the receptaculum chyli and the thoracic duct, and the connection of these with the lacteals on the one hand, and the venous system on the other, was made independently by Jean Pecquet (1622-1674), of Dieppe and Paris, and Jan van Home (1621-1670), of Leyden, whose observations were published in 1651 and 1652, respectively.
In the ancient and middle ages, the stomach was looked upon as the principal organ of digestion. The process of digestion was by some (Hippocrates and others) regarded as a coction, or πέψς (cooking), a sort of maturation effected with the aid of heat; by others it was considered as akin to putrefaction; and by still others as a mechanical process. It came to be the general doctrine that the food material absorbed from the alimentary tract was first acted upon by the liver and endowed with "natural spirits"; in the heart, by the action on the blood of the inspired air, the natural spirits were converted into "vital spirits"; finally, in the brain the vital spirits were converted into "animal spirits," which were then conveyed by the nerves to all parts of the body.
The beginnings of our modern knowledge of digestion can be traced back to the observations of the Belgian savant Jean Baptiste van Helmont (1577-1644), whose work formed a landmark in the history of chemistry. He regarded the chemical activities of the body as a form of fermentation, analogous to the familiar alcoholic or vinous fermentation; he assigned ferment action as a cause of a wide range of vital processes, thus anticipating theories that at the present time are frequently advanced. In van Helmont's view the digestion of food was accomplished by fermentative action. He recognized only two stages of digestion in the alimentary tract, namely, in the stomach and in the duodenum; the action of the salivary glands and pancreas was not 5'et known. Gastric digestion he regarded as being effected by a ferment derived from the spleen, associated with an acid principle which was necessary to its action. When the chyme passed into the duodenum the acid ferment was neutralized, and the second stage of digestion was effected by the bile.
The next developments in the knowledge of digestion came from Franciscus Sylvius (François de la Boe, or Dubois, 1614-1672), the professor of medicine at Leyden, who founded the iatro-chemical school and exerted a powerful influence as a teacher and expositor of the chemical philosophy of his time. Sylvius also attributed many of the vital processes to fermentative action; but he confused effervescence (such as occurs on adding acid to carbonate) with fermentation, and looked upon effervescence as the type of these processes. Sylvius had knowledge of two secretions, salivary and pancreatic, unknown to van Helmont.
The observations of Wharton and Stensen (published 1656 and 1662) had clarified the salivary secretion. Impressed with these discoveries, Sylvius attached an exaggerated importance to the digestive action of the saliva, and held that digestion in the stomach was accomplished much more by swallowed saliva than by any ferment of gastric origin. This view persisted for a long time.
The second stage of digestion, that taking place in the duodenum, according to Sylvius was effected by the conjoint action of the bile and the recently discovered pancreatic juice. Wirsung in 1643 had described the pancreatic duct; and in 1664 Regner de Graaf (1641-1673), of Holland, published the results of investigations on the pancreatic secretion carried out while he was a student at Leyden under Sylvius. De Graaf obtained pure pancreatic juice from dogs through quills inserted into the pancreatic duct. He fell into the error, however, of regarding it as acid; and he held, in accordance with Sylvius's theory of effervescence, that the effervescence supposed to be produced by the mixture of this acid juice with the salts of the bile was in some way associated with duodenal digestion.
In 1677, Johann Conrad Peyer (1653-1712), a Swiss, published a description of certain glandular structures discovered by him and since known as Peyer's patches. He decided that these were secretory (conglomerate) rather than lymphatic (conglobate) glands, and believed their secretion had digestive properties, active in the lower ileum at a point where the pancreatic juice must become exhausted.
In 1683, Johann Conrad Brunner (1653-1727), of Germany, published the results of experiments which he had made in exsecting the pancreas and ligating the pancreatic duct in dogs. As the dogs did not manifest any disturbance of digestion or nutrition, he argued that the importance attached by Sylvius and de Graaf to pancreatic digestion was unfounded. Brunner also showed that the pancreatic juice was not acid. In 1687 he described the duodenal glands, since known by his name, and attributed digestive properties to their secretion.
In consequence of the doubt brought by the discoveries of Peyer and Brunner, belief in pancreatic digestion waned, and for a long time the view prevailed that the stomach was the chief seat of digestion. In the latter part of the seventeenth century, two opposing theories as to the mechanism of gastric digestion were held l)y the rival physical and chemical schools of that period. The chemical theory of digestion was that of van Helmont, Sylvius, and their followers. On the other hand, Alfonso Borelli (1608-1679), the founder of the iatro-physical school, held that gastric secretion was chiefly effected by powerful triturationof the ingested food by the muscular walls of the stomach, as appears especially in birds; and while he conceded a corrosive action of the stomach juices in some species, his followers denied all chemical digestion and regarded the whole process as purely mechanical.
During the eighteenth century the only additions to the knowledge of digestion were a few studies of the gastric juice.
René Antoine Ferchault de Reaumur (1683-1757) developed a new and fruitful method of investigation, publishing his results in 1753. He introduced metal tubes containing various food materials into the stomach of a buzzard (which, like other carnivorous birds, ejects from the mouth indigestible substances like bones, etc.) and other animals, and on examining them subsequently was able to determine the effect of the gastric juice on these materials. By using sponges in the tubes he was the first to obtain gastric juice in pure condition. He observed that meat and bone were dissolved by the gastric juice, but not grains or flour. He thus demonstrated that this secretion possessed a definite solvent power, distinct from putrefaction, and independent of trituration.
Employing Reaumur's and other similar methods, Lazaro Spallanzani (1729-1799), of Italy, continued and extended the observations, publishing his results in 1777 and subsequently. In 1777 Stevens, of Edinburgh, published a similar research. John Hunter (1728-1793) in 1773 and 1786 also published some observations on digestion.
The acidity of the gastric juice, appreciated by van Helmont and denied by his successors, was not generally recognized until the nineteenth century. Spallanzani and Hunter regarded the acidity of some of the specimens which they obtained as occasional or exceptional or abnormal only. Carminati recognized the real conditions, showing in 1785 that the gastric juice while fasting is neutral, and is acid only after taking food; his observations, however, did not gain general attention,
A contribution of interest to Americans, which, however, passed unnoticed, was the graduation thesis of John R. Young, of Maryland, at the University of Pennsylvania in 1803, in which he described experiments made on digestion in the stomachs of frogs and human subjects, and demonstrated the acidity of the gastric juice.
The foundations of our present knowledge of digestion were mainly established during the second quarter of the nineteenth century.
William Prout (1785-1850), of London, in 1834 identified the acid principle of the gastric juice as hydrochloric acid.
William Beaumont (1785-1853), an American army surgeon, from 1825 to 1833 conducted a celebrated series of observations of gastric digestion through a fistula following a gunshot wound in the case of the Canadian Alexis Saint Martin, the results being published in 1833, These observations constituted an important contribution to the subject and attracted world-wide attention.
Leuchs in 1831 discovered the starch-digesting properties of saliva. Payen and Persoz in 1833 discovered and studied the amylolytic ferment diastase in germinating barley. Mialhe in 1845 isolated ptyalin from saliva.
J. N. Eberle in a work published in 1834 was the first to note the power of an extract or artificial gastric juice prepared from the gastric mucous membrane to dissolve proteid material. He, however, erroneously attributed this solvent action to the mucus on the surface of the stomach. Theodor Schwann (1810-1882), the discoverer of animal cells, investigated the subject (partly in association with his teacher Johannes Müller) and in crude form isolated from the gastric mucosa a principle possessing intense proteolytic powers, to which he gave the name pepsin; his results were published in 1836.
In his treatise published in 1834 Eberle noted the fact that a watery extract of the pancreas would emulsify oil, and he surmised that one of the functions of the pancreatic secretion was to favor the absorption of fat. In 1836 Purkinje and Pappenheim discovered that extracts from the pancreas possess proteolytic properties. In 1844 Valentin made some observations on the starch-digesting powers of the pancreatic fluid; and in 1845 Bouchardat and Sandras definitely demonstrated the secretion of an amylolytic principle by this organ.
Following these pioneer discoveries, the elucidation of the functions of the pancreas, especially its fat-splitting action, was accomplished chiefly by the work of the French investigator Claude Bernard (1813-1878), whose researches on this subject were prosecuted about 1836-1846.
From these beginnings the chemistry and physiology of digestion have been further elaborated by numerous subsequent investigators.
The study of gastric digestion was made a simple clinical procedure by the employment of the stomach tube for obtaining samples of gastric juice. This originated with Adolph Kussmaul (1822-1902), who in 1869 reported the use of the stomach tube in the treatment of dilatation of the stomach; subsequent to which the examination of gastric juice for diagnostic purposes was elaborated by W. O. Leube, C. A. Ewald and Franz Riegel, and their associates during the seventies and eighties of the last century.
Important studies of the action of the digestive organs were not long ago made by Ivan Pyotrovich Pavloff (often transliterated, from the German, J. P. Pawlow) (born 1849), director of the Imperial Institute of Experimental Medicine in Saint Petersburg, the results of whose brilliant researches (conducted 1887-1897) were first published in collected form in 1897. For this work Pavloff received the Nobel prize in 1904.
The discovery of pancreatic secretin by William Maddock Bayliss and Ernest Henry Starling, announced in 1904, opened up an entirely new field of knowledge, that of the action of the so-called hormones as inciters of secretory activity carried to the points of action by the circulation.
The introduction of the X-ray made available a new and fertile method of studying the movements of the digestive organs; one of the earliest and most prolific workers in this field has been an American, Walter Bradford Cannon, professor of physiology at Harvard, whose contributions on this subject date from 1899.
The main basis of dietetics rests in the chemistry of food and nutrition. This knowledge could not be developed until the science of chemistry entered upon its renaissance, which occurred much later than the birth of modern anatomy, physiology and physics. The discovery of oxygen in 1774 opened the way to a rapid development of chemical knowledge, just as Harvey's discovery of the circulation a century and a half before had been the starting point for physiology.
As has been the case with many other discoveries, the effective discovery of oxygen had been anticipated long previously by work that had fallen into oblivion. In 1668 a young Englishman at Oxford, John Mayow (1645-1679), published a remarkable work in which he argued that the atmosphere contains, as he styled it, an "igneo-aereal" or "nitro-aereal" principle which by combining with combustible ("sulphureous") substances constitutes the process of combustion; that this principle is imparted to the blood by the respiratory activities; that the union of this principle, carried in the blood, with combustible material in the muscles gives rise to muscular action and is a source of animal heat. Though this theory was soon forgotten, it was a remarkable presentation of the doctrine of oxidation (including body oxidation as the source of animal energy), and anticipated by a century the discovery of oxygen.
In 1774 oxygen was independently discovered by Joseph Priestley (1733-1804), an English clergyman, and by Karl Wilhelm Scheele (1742-1786), of Sweden. It was Antoine Laurent Lavoisier (1743-1794), of Paris, however, who grasped the real significance of this discovery, and by his researches, published from 1775, overthrew the false though fruitful phlogistic theory of heat that had dominated chemistry for a century, and showed the true nature of combustion and the properties of oxygen.
Lavoisier was followed by a number of brilliant investigators, who rapidly laid down the great foundations of chemical science. The beginnings of organic chemistry may be traced to some of these early workers; Lavoisier, for instance, showed that organic compounds are composed mainly of carbon, hydrogen and oxygen, and sometimes nitrogen.
The foundation and elaboration of organic chemistry was mainly the great achievement of the illustrious chemist Justus Liebig (18031873). After studying chemistry at Paris under Gay-Lussac, he was professor of chemistry at Giessen 1824-1852, and at Munich from 1853 until his death in 1873. About 1837 he began epoch-making investigations of physiologic and organic chemistry, and in works published from 1840 he laid down the main lines of our knowledge of the chemistry of food and nutrition. He first, for instance, sharply differentiated the foodstuffs albumen, fat and carbohydrate, and recognized the tissue-forming function of albumins and the heat-producing properties of fats and carbohydrates.
Since the time of Liebig many workers have brought our knowledge of the chemistry of food to its present state. Among important investigations of this character now being actively prosecuted are those on the molecular structure of the complex foodstuffs, such as the studies of Emil Fischer, Emil Abderhalden and others on the proteins. Some of the sugars have been artificially synthesized, and a beginning has been made even on the proteins.
Crude attempts at food analysis date back for centuries, as in connection with governmental measures to prevent adulteration of foods and beverages. In the modern era George Pearson, of England, in 1795 reported an analysis of potatoes; in 1805, Einhoff analyses of potatoes and rye. Eeliable analyses of milk were reported by Peligot in 1836, and of feeding stuffs and milk by Boussingault and Le Bel 1836-1839. From about 1840, through the work of Liebig a great impetus was given to food analysis; and with the further advances of chemistry came the development of reliable analytic methods and the accumulation of data. From about 1860 the standard methods of food analysis now employed were developed by Wilhelm Henneberg (1825-1890), of the agricultural experiment station at Weende, near Göttingen; these methods soon came into general use and have greatly facilitated and systematized this line of work.
Possibly the earliest analyses of food made in the United States were of some cereals by C. U. Shepherd published in 1844. Analyses of various foods were published by Salisbury in 1848, Beck in 1848-1849, Emmons in 1849, Jackson in 1857. One of the most prolific workers in this field in this country was Atwater, who, employing the Weende methods, made analyses of maize in 1869, and commenced an extended series of analyses of fish and other foods in 1877.
Dietary studies—investigations of the amounts of foodstuffs actually consumed by different classes of people under various conditions—furnish an important part of the data underlying the science of dietetics. Among the earliest investigations of this sort were those conducted by Liebig in 1810; by Beneke in England in 1851; and in this country by John Stanton Gould in 1852 and Atwater in 188G. Since then many such studies have been made and a large amount of information collected.
A knowledge of the processes of metabolism forms another component of the foundations of dietetics.
Probably the earliest real metabolism studies were prosecuted by Sanctorius (1561-1636), who published his results in 1614. Sitting in a chair suspended from steelyards, he observed the changes in weight from eating and from the loss of insensible perspiration.
Theories of the source of animal heat were presented from the early days of physiology. Van Helmont held that animal heat was generated by fermentation of the blood in the heart. Sylvius believed it to be produced by the supposed effervescence resulting from the mixture of venous blood with acid chyle. Mayow in 1668 anticipated the modern view that the body energy is derived from oxidation in the tissues; but his views were soon forgotten. Toward the end of the seventeenth century these chemical theories were largely superseded by the physical view that animal heat is generated by the friction of the blood in the capillaries. It was not until after the discovery of oxygen that our present conceptions of the part played by oxidation as the source of animal energy were founded by Lavoisier.
The general outlines of our knowledge of metabolism were formulated by Liebig, the details being worked out by numerous subsequent investigators, many of them under his personal influence. In this way, chiefly since 1850, an extensive mass of data on this subject has been accumulated. The earliest metabolism study appears to have been one by Lehmann, made in 1839. The study of the metabolism of nitrogen is a comparatively simple matter, and has been an easy and frequent subject for investigation.
The determination of the exchanges of carbon and hydrogen is a much more difficult matter, involving the collection of the products of respiration and requiring elaborate apparatus and an amount of labor rarely available. Early respiration experiments with animals were made by Boussingault about 1844, Bidder and Schmidt in 1847-1850, and Regnault and Reiset in 1849; and with man by Barral in 1847-1848, and Hildesheim in 1856.
A most extensive and accurate series of investigations was conducted by Max von Pettenkofer (1818-1901) and, especially, Carl von Voit (1831-1908), in the Physiological Institute at Munich with the respiration apparatus constructed by Pettenkofer about 1860. Animals and men were made the subjects of extended observation with this apparatus from 1861 to 1867, and principles of fundamental importance were established by these classical researches.
Other important studies of metabolism were prosecuted by Pflüger and his associates in Bonn, by Zuntz in Berlin, by Tschudnovski, Pashutin, and others in St. Petersburg, by Tigerstedt in Sweden, and by many others.
The energy exchanges of the organism have a fundamental bearing in dietetics, since the heat output of the body under different conditions determines the caloric requirements of the diet. The apparatus used to investigate these exchanges, the respiration calorimeter, besides measuring the respiratory products after the manner of Pettenkofer's apparatus, determines with great accuracy the amount of heat given off by the subject. In its perfected form this mechanism is a marvel of complexity, elaborateness, and delicacy, requiring much labor and ample resources for its construction and operation.
Some imperfect calorimetric studies on animals and man were published by Russian observers from 1884. Max Rubner (1854-) was the first to conduct a successful and elaborate series of calorimetric observations on animals. He was educated at Munich under Toit; professor at Marburg 1885-1891; at Berlin from 1891, succeeding Koch as Director of the Hygienic Institute. His studies were begun about 1889, and his results published in full in 1902. He demonstrated that the law of the conservation of energy holds good for animals; and he has laid down principles fundamental in this branch of physiology and of the utmost importance in dietetics.
The most elaborate calorimetric investigations ever carried out have been those prosecuted in this country since 1892 by Wilbur Olin Atwater (1844—1907) and his associates and successors. Atwater studied at Munich under Voit, and derived some of his ideas from Rubner. Professor of chemistry at Wesleyan University, Middletown, Connecticut, from 1873 until his death, he devoted his whole life to investigations concerning food and nutrition. In 1892, with the assistance of the physicist Rosa, he began the construction at Wesleyan University of a respiration calorimeter large enough to accommodate a human subject. This apparatus underwent gradual improvement until finally direct determinations of the oxygen exchanges were, for the first time on a large scale, carried out. The work was jointly supported by Wesleyan University, the Storrs (Connecticut) Agricultural Experiment Station, the United States Department of Agriculture, and (later) the Carnegie Institution. With this apparatus an elaborate series of researches was carried out from 1892 to 1907, the results of which must stand as classical. After Atwater's death in 1907, the original apparatus was removed to Washington and installed in the Department of Agriculture, where it is now in operation; while his successor Francis Gano Benedict under a grant from the Carnegie Institution is continuing the research with an equipment constructed in Boston.
Other investigators have since taken up this line of work, and important points concerning metabolism under different conditions and in various morbid states are now in course of elucidation.
To recount all the important researches on the physiology and chemistry of dietetics would unduly prolong this historical review. I have mentioned the principal contributions that have first opened up the various lines of inquiry pertinent to the subject. By the researches of a host of investigators along these lines have been accumulated the data and developed the principles that underlie the theory of dietetics as we have it to-day. The evolution of the subject is still far from complete, and points of even fundamental importance are yet to be worked out. So elementary a standard, for example, as the optimum daily ration of protein, is even yet unsettled. The establishment of rational principles of feeding in disease has been very incompletely accomplished. The whole subject is in a transitional stage; investigation is, however, proceeding rapidly, and results with important practical bearings are being constantly gained.
Americanto the subject have been noteworthy, such as the work of Beaumont, Atwater and Cannon. Honor is especially due to the United States Department of Agriculture for the special encouragement it has since 1894 given to the study of problems relating to the food and nutrition of man; under its auspices a vast amount of research has been systematically fostered all over the country and the results published and distributed in an extensive series of bulletins.
The scientific and rational principles of dietetics have not become well assimilated into the conceptions of the public, or even of the medical profession. Dietetics is a fruitful field for fallacy, fancy and fad. There are a few diseases that have a specific dietetic treatment, such as diabetes, acidosis, scurvy, beri-beri, gout, etc., in which, as also in infant feeding, the profession follows rational principles. With many diseases the appropriate dietetic principles are ignored, or have not been as yet worked out, or do not differ from those of health. In this field the dietetic management is to a certain extent a matter of caprice, guesswork and error. Faulty practises are in vogue, such as the general use as food of meat extractives and soups, although well known to be devoid of nutritive value. Mystic potencies and occult dangers are erroneously ascribed to articles of food. The distrust of food engendered in the ancient days of medicine still lingers, and there is no doubt that countless lives have been sacrificed to the fear of feeding in disease.
The medical students and practitioners of the present and future need to be more thoroughly grounded in the scientific and rational basis of dietetics. Only by a thorough appreciation and application of its principles can this subject be raised from a position of empiricism to that scientific dignity which it is the aim of modern medicine to attain, or the powerful agency of diet be utilized in its maximum efficiency for the benefit of mankind.