By William A. Albrecht, PhD
Summary: Today, the standard explanation for tooth decay goes something like this: a carbohydrate-rich film develops on the teeth; bacteria in the mouth feed on that carbohydrate; acid produced by the bacteria attack and degrade the teeth. Yet this explanation fails to account for numerous observations regarding cavity development, which, as many nutritionists of the early twentieth century showed, appears to have more to do with systemic nutritional deficiency in the body than a localized pathogenic assault. In this fascinating 1947 article, renowned agronomist Dr. William Albrecht adds weight to the malnutrition theory of tooth decay, correlating regional differences between soil fertility, plant constitution, and dental health in America. In short, he concludes, the more fertile a soil, the fewer cavities in people who eat food grown in that soil. With tooth decay the most common and widespread degenerative disease in the United States—just as it was in Dr. Albrecht’s day—it seems obvious that brushing carbohydrates off of our teeth is not enough to prevent cavities. We need nutrient rich foods, produced by fertile soils, to thwart oral bacteria from proliferating in the first place. From the Annals of Dentistry, 1947. Lee Foundation for Nutritional Research reprint 37.
[The following is a transcription of the original Archives document. To view or download the original document, click here.]
Our Teeth and Our Soils
The knowledge about the human body and its many functions has been accumulating seemingly very slowly. The additions to our information have awaited the coining of each new science and the contributions by them in their respective fields. Dentistry as well as the medical profession have been ready and quick to accept and use any new knowledge that might alleviate human suffering.
In medicine, for example, one can list the major successive additions almost as separate sciences, coming at the slow rate of about one per century. Anatomy was the beginning one, making its debut in the sixteenth century. The seventeenth century brought us physiology; the eighteenth added pathology; and the nineteenth emphasized bacteriology—all these for our better health.
Very probably the twentieth century will be credited with the addition of the science of nutrition as a major contribution to the better life of our people. Better nutrition is leading us to think less about medicine as cures and less about fighting microbes with drugs. In a more positive way, it is helping us to think more about helping the body defend itself by being well fed and therefore healthy.
If we are to bring about good nutrition by means of good food to build up a good defense for the body, then that defense must be strong, not only against enemy invasions, as it can be against tuberculosis, but also against the degenerative diseases such as heart troubles, cancer, diabetes, etc. For such defense, then, of necessity, the science of the soil and its fertility–by which alone high-quality foods can be provided—may well be an addition during the present century to our knowledge of the better functions and better health of our bodies.
It is proposed therefore in this discussion to lead you to think about the health condition of only one part of our body, namely, our teeth, as they are related to the fertility of our soils.
Some Basic Facts Involved
In dealing with the subject of soil fertility and its implications for our teeth—or for any other part of our anatomy and our physiology—it is essential that one establish certain facts and principles at the outset and then follow through, as these seem to have causal connections with the phenomena under consideration.
The first fact that may well be considered is the observation that under moderate temperatures an increase in annual rainfall—for example, from 0 to 60 inches, as is the range in going across the United States from near the Coast Range eastward—gives first an increased weathering of the rocks. That change represents increased soil construction. Going east from zero rainfall means increasingly more productive soils until one reaches about the midcontinental area. Then with still more rainfall there comes excessive soil development, under this higher rainfall, which means increased soil destruction in terms of soil fertility considered both in quantity and in quality.
The second important fact in connection with this climatic pattern of soil development is the observation that at the maximum of soil construction (and in the approach to it), which is near the 100th meridian of longitude, there is a wide ratio of the exchangeable calcium to the exchangeable potassium in the colloidal clay of the soil. There is a similar ratio of these two in the chemical composition of the crops and other vegetation grown thereon.
Then there is the third significant fact, namely, that calcium is associated with the synthesis of proteins by plants, while potassium is associated with their synthesis of carbohydrates. The latter process, which is commonly spoken of as photosynthesis, may well be considered a suprasoil performance. This classification is proper since photosynthesis is a compounding of carbon, hydrogen, and oxygen—all weather-given elements taken from the air and water—into carbohydrates by sunshine energy.
The process of synthesizing proteins is, on the other hand, a biosynthetic process, that is, one [fueled] by the life processes of the plant. It seems to be a case in which some of the carbohydrates serve as the raw materials out of which the proteins are made. This is brought about by combining with these carbohydrates some nitrogen, some phosphorus, and some sulfur, all coming from the soil. At the same time, some calcium and possibly several other soil-borne nutrient elements are required as more of the carbohydrates are consumed as energy materials for this conversion process.
The fourth significant truth that brings soil fertility into control of the composition of our food and therefore of our health comes out of the facts that a) in soils under construction by the limited climatic forces, or those with a wide calcium-potassium ratio, proteinaceous and mineral-rich crops and foods as well as carbonaceous ones are possible and b) in soils under destruction by excessive climatic forces, or those with a narrow calcium-potassium ratio, protein production is not so common, while production of mainly carbohydrates by the crops is almost universal.
Out of these climatic, pedologic, and physiological facts, there comes the major principle of concern to the dentists, namely, that in regions of higher rainfall we have excessive carbohydrates in nature and therefore may expect them in the human diet. Where rainfall is high enough to encourage vegetation in abundance, we have a hindrance to sound teeth from Nature herself, because too much carbohydrate—or, conversely, insufficient proteins and minerals—militates against sound teeth, a fact all too familiar to those in the dental profession.
We need then to realize these facts and consider them by remembering our geographic location in our management of the soil with human nutrition in mind.
Excess of Carbohydrates Is Natural
In considering soil fertility as it provokes excessive carbohydrates and deficiencies of proteins and minerals, we need only to look at the chemical composition of the human body in comparison with that of plants (Table 1).
Table I. Chemical Composition of the Human Body in Comparison with That of Plants and Soils
|Source||Element||Percent Weight of Human Body||Percent Dry Weight of Vegetation||Percent Dry Weight of Soil*|
|Air & Water:||Oxygen||65.00||42.9(2)**||47.3|
|Air & Soil:||Nitrogen||3.0||2.63(4)||–|
|Copper||Very small amount||0.0011||–|
|Zinc||Very small amount||0.0041(13)||–|
|Fluorine||Very small amount||0.0005||0.10|
|Aluminum||Very small amount||–||7.85|
*Collected from various sources.
**Order of magnitude [sic].
***Percent readily exchangeable in soils.
From these analytical data, we can see that of all the minerals plants take up from the soil, potassium is taken in the largest amounts, while calcium and phosphorus are next in that order. In the human body, these same elements are the major three, but calcium is first, phosphorus is second, and potassium is third.
Of amounts still higher than any of these in the human body is nitrogen. This is the key element distinguishing protein, synthesized as amino acids from the elements only by plants. [Yet] plants offer us mainly carbohydrates with only small amounts of proteins. [Therefore] plant composition, considered as our food, presents possible shortages of proteins, of calcium, of phosphorus, and of probably other essential elements.
We, like other animals, are constantly in danger of deficiencies of proteins and minerals, especially as we are more vegetarian [sic]. By the very nature of the creative processes that start with the soil, carbohydrates are plentiful, while there are deficiencies of minerals and proteins. Man is therefore always faced with the shortages of minerals and proteins relative to the carbohydrates and fats. It is this nutritional need that encourages his carnivorousness and his use of animal products such as eggs and milk.
Excessive Carbohydrates Are Invoked by Our Fertility Pattern
That these shortages of minerals and proteins vary according to the pattern of soil fertility is demonstrated very clearly by the soils of the United States. The lower rainfalls of the western half of our country (the area of sparse population) have not removed the calcium and the other nutrient cations from the surface soil. These lime-laden, mineral-rich areas have been the prairie soils. It is on these that the legumes—as protein-rich, mineral-providing forages—flourish widely and profusely. It is these soils that were feeding buffaloes in the early days by their grass, without purchased protein supplements. It is these soils that are giving us protein products in beef and lamb today.[Four figures showing data maps of the United States, with captions as follows. See original for images and data.].
Figure I. Distribution of mean annual precipitation in the United States. The higher rainfalls in the eastern United States have leached the minerals from the soils, hence forests, in early days, and carbohydrate-producing crops today—more than protein-rich, mineral-rich products—grow there.
Figure II. The lines of constant ratios of rainfall to evaporation (times 100) give pattern to the fertility of the soils. They tell us, for example, that the Corn Belt soils are similar to those farther west under less leaching. They are therefore still well supplied with minerals. (According to Professor Transeau, Columbus, Ohio.)
Figure III. Climatic and vegetational soil groups in the United States (Marbut, 1935). The soil map shows itself [to be] a composite of the map of rainfall and the map of rainfall evaporation ratios. It is the soils that give us an East and a West and divide the East into a North and a South.
Figure IV. Climatic and vegetational soil groups of the United States (Marbut, 1935). The pattern of soil development of the United States shows the maximum soil construction [occurs] in the midcontinental area. It is on the soils there that maximum protein and mineral delivery by crops is possible as good feed and food.
Looking at the eastern half of the United States (the area of densest population), this part of our country, with its higher rainfalls, has soils leached so highly that most of the calcium has gone from them to the sea. In fact, that loss of calcium has made us classify them as “acid soils,” as if the acidity—rather than the shortage of fertility—were responsible for their failure to grow protein-rich legumes. These soils were originally growing only wood as forests. [Having been] cleared of these, they have [since] been growing starchy crops. It is on these eastern soils that we fatten the cattle that are born and grown on the soils farther west. These eastern soils can still grow hogs, whose carcasses are mainly fat.
Such soils, if given fertility treatments, can produce proteins by reproducing and growing the animals themselves but usually only with much help by attending veterinarians. Eastern United States is an area of increasing troubles with our dairy cattle, such as what is called “brucellosis” when affecting the cows and “undulant fever” when it is of the human. Both of these diseases are still baffling to the diagnostic efforts aiming to locate their fundamental cause. If the Creator himself was making only carbonaceous products such as forests on those soils, shall we not believe that such products must represent about the limits of our possibilities when we take over and grow crops on them without adding fertility to the soil?[Six figures with captions as follows. See original for images.]
Figure V. [Image of four plants ranging in level of growth, with leftmost plant smallest and rightmost plant largest.] “To be well fed is to be healthy” is the case of plants as well as humans. More clay, though acid, put into the sand (increasingly from left to right) made healthier plants.
Figure VI. [Image of four rows of spinach plants.] Spinach fertilized with more nitrogen and calcium to make it more proteinaceous (right two rows) was protected against attack by the thrips insects, while spinach less rich in proteins (left two rows) was not.
Figure VII. [Map showing by region the protein content of wheat grown in Kansas.] Protein Content of Wheat—Kansas 1940 (as indicated by preharvest survey conducted by agricultural marketing service, United States Department of Agriculture). The protein concentration in wheat of Kansas increased from 10 to 18 percent in going from the eastern part of the state, with 37 inches of rainfall, to the western part, with only 17 inches. Plants can manufacture proteins only as the fertility of the soil permits.
Figure VIII. [Image of porcupine eating a pair of discarded antlers.] Wildlife struggles desperately to get its calcium and phosphorus, as shown by this porcupine consuming antlers in the Northern Woods.
Figure IX. [Map showing by state the relative change in production of pigs from immediately before World War II to 1947.] Map of the Pig Crop—With States Sized To Give All Pigs Equal Space. The eastern states produce carbohydrates more than proteins, to make [their] animals those with more fat than protein. (Map prepared by American Meat Institute. Source of data: USDA.)
Figure X. [Map showing by state the relative change in production of cows from immediately before World War II to 1947.] Beef Cows—Where They Are, How They Have Increased Since Prewar. The western states produce mineral-rich, proteinaceous forages, to make [their] animals those with more protein than fat. (Map prepared by American Meat Institute. Source of data: USDA.)
Soil Exhaustion Spells Deficiencies of Proteins and Minerals but Excess of Carbohydrates
Soils naturally highly weathered are no longer well stocked with nutrient mineral reserves in their sand and silt fractions nor with mineral fertility adsorbed on the clay. Such soils must of necessity give crops and foods that are mainly carbohydrates and are therefore deficient in proteins and minerals. But quite the opposite, the less weathered soils, under low annual rainfalls, are mineral rich in the silt and sand reserves and on the clay. Hence, they give both proteins and minerals, along with carbohydrates, in the plants grown on them.
In these facts we have the suggestion that any soil undergoing exhaustion of its fertility, whether by nature or by man, is bringing about a change in the chemical composition of any plant species growing on it. This change means that the plant species become more carbonaceous, less proteinaceous, and less mineral rich. These changes occur within any single plant species—too commonly believed constant in its chemical composition regardless of the soil growing it.
Surveys and Experiments Demonstrate the Facts
That we may well take cognizance of this as a principle has been demonstrated by the study of the chemical composition of many crops and other plants native to soils that are (a) slightly (b) moderately, and (c) highly developed under increasing rainfall and temperature.
While some thirty plant species common on the slightly developed soils contained enough calcium, phosphorus, and potassium in total to make up almost 5 percent of their dry weight, this figure dropped to 4 percent in going to a similar number of plants native to moderately developed soils. It then dropped to less than 2 percent in going to plants natural to highly developed soils. As the soils are more highly developed, then, or farmed under higher rainfall and temperature, they provide us, through the plants on them, less and less of these minerals essential for bone growth and less of those associated with synthesis of proteins by the plants.
Experiments by Dr. E.R. Graham at the Missouri Agricultural Experiment Station have demonstrated how less calcareous soils make less proteins and more carbohydrates—or that the changing calcium-potassium ratio of higher development of the soil brings corresponding decreases in the protein and mineral contents in the same kind of vegetation. He grew soybeans on soils with a (1) wide (2) medium, and (3) narrow ratio of calcium to potassium. He reproduced the conditions of soils under increasing weathering, or under increased experience with rainfall and temperature. These three soils represented increasing encouragement for the plants to produce carbohydrates more than to synthesize proteins.
This narrowing ratio of calcium to potassium resulted in an increase of vegetative bulk by one-fourth. Such an increased tonnage would warrant agronomic applause. But this increase in vegetative mass represented a reduction in the concentration of protein by one-fourth, a reduction in the concentration of phosphorus by one-half, and a reduction in the concentration of calcium by two-thirds of that in the smaller-tonnage yield.
By modifying the relative amounts of calcium and potassium in the soil much as they are modified under increasing weathering of the soil, the physiology of the plant was shifted to the production of less protein and more carbohydrates. Higher soil development and more rainfall and temperature, then, bring less protein production by any crop and therefore less proteins and minerals in our feeds and our foods.
Figure XI. [Photo of two samples of wool. See original for images.] Animal products reflect soil deficiencies more than the animal body or the plants. The wool on the left, which could not be carded, was grown by sheep fed lespedeza fertilized by phosphate only. The wool on the right, which carded nicely, was from sheep fed similar hay grown on soil given both lime and phosphate.
Concentration of Protein in Our Food Crops Is Being Lowered by Soil Exhaustion
As our soils are being exhausted of their fertility by cropping under the intense economic pressure now being put on them, a single grain crop such as wheat is producing less protein and more starch as time goes on; we say, “Wheat is becoming soft where once it was hard.” In our near-colonial days, we produced hard wheat in the valley of the Geneseo River of New York. That wheat basket—or breadbasket of this country at that time—made Rochester the “Flour City.”
Today, Rochester is still the “Flower City,” with its many parks, but the “hard” wheat has moved westward across the United States, while the “soft,” starchy wheat—which we seemingly desire for our pastries—is crowding along in its wake. Soft wheat has now gone so far west that even in Kansas the millers and bakers are complaining about its low protein content and their low volume of bread output per unit of flour used. The farmers of Kansas, however, are delighted with the high volumes of output, as bushels per acre, that are possible when the plants [make] only carbohydrates instead of converting these into protein—of much less bulk as plant output.
Corn too is doing less in its synthesis of proteins. While we have pushed up the volume of its output as bushels per acre by hybrid vigor, we have not realized that the concentration of protein in our corn grain has been dropping, from a mean figure of about 9.5 percent to only 8.5 percent during the last ten years.
Forage crops, along with grain crops, have been going to lower concentrations in minerals and proteins. They have been going lower in giving us what may be called the “grow” foods but have been holding up in supplying for us what may be called the “go” foods, namely carbohydrates. But as this happens, there is greater deception by the crop, of which only vegetative mass is of concern or measured, than when the harvest considered is the seed or the plant’s efforts for its own reproduction and continuance of the species. As we harvest vegetative bulk, we fail to note the low delivery of protein, which reports itself as lowered grain yield more noticeably than as less vegetative bulk.
Also, as we mine the soils of their fertility so that the output by one crop as bulk goes down, we search the world and bring in some exotic crop because it can make tons or bushels where the preceding crop failed. If this imported crop makes vegetative tons where the others failed, it must be putting out its products with less of the soil’s fertility in them, and therefore they must be more carbonaceous and probably of deceptive nutritional values.
As a consequence of the lowered protein concentration in grains and grasses under soil fertility depletion, we have had not only the westward march of “hard” wheat and the clamor for more “grass” agriculture, but also a westward march of our protein in beef and lamb. Chicago is no longer the major beef cattle market. That honor now rests on Kansas City. Even the hog market, a trade mainly in fat products, has moved to central United States, when it once was farther east. These movements have been under the force of a declining soil fertility and are not merely the result of man’s wanderlust or his nomadic nature.
Here, then, in the soil fertility, is the pattern of the nutritional values of our foods and feeds pointing out their lowered concentrations of minerals and proteins. Here is the lowered power of growth and lowered capacity for reproduction. Life is not passed from one fat globule to another, nor from one starch grain to another, but only from one protein to another protein molecule. Can a dentist see good permanent teeth being laid down in the jawbone of a fetus when the mother’s diet is deficient in minerals and protein? Can he find sound teeth in schoolchildren when carbohydrate bulk predominates in their diet because of its lesser cost and easier storage than that of milk and meat? Is it any wonder we were startled when Colliers told us of “The Town Without a Toothache,” located in a region of lower rainfall? [See this in-depth article about Hereford, Texas, the town once famous for its complete lack of tooth decay.]
Geography of Dental Defects in the United States and the Pattern of Soil Fertility
That Hereford, Texas, is in the part of the United States with highly fertile soils is not so startling when the geography of dental defects on a larger scale is considered. The recent physical examinations of the millions of men taken into the U.S. Army and Navy give a wealth of data in relation to the many possible factors in control of our health and of the condition of our teeth. These data may well be correlated with the fertility of the soil for their suggestive value in listing many of our health troubles as possible deficiencies originating in the soil. In these data and records, there is an opportunity to relate the caries of the teeth to the soils of the United States according to the soils’ pattern of fertility, or to their degree of development by the climatic forces.
Very recently, Commander C.A. Schlack and Lieutenant Birren of the U.S. Navy Medical Research Institute presented some data by regions of the United States that represented the condition of the teeth of 69,584 men coming on active duty in the Navy in 1941–42 (C.A. Schlack and J.E. Birren, “Influences on Dental Defects in Navy Personnel,” Science, 104:259–262, 1946). These represented 93 percent of a lot from which 7 percent had already been eliminated for dental reasons. This screening reduced the regional differences, but even in spite of this, those regional differences show a decidedly interesting relation to the development of the soil.
From the report of these naval officers, one is almost astounded at the poor dental condition in this sample of our people. It is especially serious given that these naval inductees represented, on the mean, the youthful age of twenty-four years, with 82 percent of them below the age of thirty years. For the group as a whole, the report reads as follows: “The mean number of simple and compound cavities was found to be about ten per person…and five fillings per person [were also counted]…Few teeth required extraction, despite the large number of carious teeth, the mean number per person being about 0.2. In contrast the mean number of missing teeth was 4.7 at the time of the examination.”
This is a sad commentary on the dental condition of our young men, when the statistics list for them an average of fifteen carious areas each—in spite of the regular encouragement by the radio to use the toothbrush daily and to “see your dentist twice a year.” But when the chemical composition of our teeth tells us that they consist mainly of calcium phosphate, and when the foremost fertilizer treatments needed to grow even carbonaceous vegetation on our soils are lime (calcium) and superphosphate (phosphorus), there is good reason that the poor dental condition of these naval inductees should be connected with the low fertility of these soils. When soils need lime and phosphate to grow agricultural vegetation, much more will they need these fertilizer additions of calcium and phosphorus in order to pass these nutrient elements onto the animals and the humans in the chain of decreasing chances to get these soilborne requisites for good, sound teeth.
In recalculating the dental data of these naval inductees so as to make them represent more nearly the soil areas according to increasing degrees of soil development in going from the arid west to the humid east, the correlation is very striking. It is highly significant that the lowest numbers of carious teeth are in the longitudinal belt of dual-state width just west of the Mississippi River. Hereford, Texas, is included in this belt. As one goes either westward or eastward from this belt to other, similar belts, tooth troubles increase. This increase, however, is much larger in going eastward, that is, to the excessively developed soils under higher rainfall and temperatures, than it is in going westward to the underdeveloped soils.
Figure XII. [Map correlating dental caries rates and soil zones in the United States. See original for image and data.] The concentration of dental caries gives a curve reciprocal to that of soil development under the climatic forces. The minimum of caries occurs in the midcontinental area, the area of maximum soil construction. Caries increase going westward from there, to soils less developed, and increase even more so going eastward, to soils more highly developed.
Here is a clear indication that those soils with a high capacity for protein production, because of their high mineral fertility, are the soils that have also grown better teeth. These are the soils of the open prairies. Quite differently, those soils that have a low capacity for producing legumes, beef, and mutton, that have been growing starchy grains and fattening the livestock, have a much higher number of carious teeth per person. These are the soils of the forested areas, or the potential producers of mainly fuel foods.
The maximum number of caries was exhibited by the men from the New England states, where the cavities amounted to 13.5 per person, accompanied by 7.8 fillings, for a total of 21.3 carious areas per mouth. With such numbers of defects, it seems a pity that we can’t have more than thirty-two adult teeth. In the Middle Atlantic states, just south of New England, the total figure was 19.6. Still farther south, the corresponding value was 13.4, of which 9.7 were cavities and 3.7 were fillings.
In this case of the soil and teeth as one goes south from New England, there are three factors that may help explain the decrease in caries. There is, first, a decreasing ratio of rainfall to evaporation and therefore less relative leaching of the soil; second, there is less acidity to break down the mineral reserves, because of the nature of the clay; and third, in the South there is the more general use of fertilizers consisting mainly of carriers of calcium and phosphorus.
In these regional data, there are the suggestions that the curve [representing] the condition of the teeth is the reciprocal of the curve of the fertility of the soil. We may expect also from these relations that the pattern of soil fertility is in control of not only the health of the teeth, but also of health in general. This is strongly suggested by a careful study, reported by Dr. L.M. Hepple of the University of Missouri, of the more than 80,000 draftee rejections from more than 310,000 selectees for the Army from Missouri alone.
He points out, for example, that Kansas had lower rejection rates than Missouri. This is another way of telling us that the health troubles increase in going from the calcareous soils of Kansas to the lime-deficient soils of Missouri. Equally interesting in terms of draftee rejections are his data going across Missouri from the northwest to the southeast, which means going from the legume and cattle area to that of cotton. His series of figures for draftee rejections in making that traverse of the state was 208, 247, 280, 339, and 368 per 1000 selectees. Even for an area so limited as Missouri, the health condition in terms of Army standards reflects the pattern of the fertility of the soil.
From all of the data of the inductees into the Army and the Navy, there is the suggestion that more of our so-called “diseases” may well be statistically mapped for the United States and compared with the map of the soil fertility. If all other body irregularities, as well as those of the teeth, were so viewed, it is highly probable that many of our diseases would be interpreted as degenerative troubles originating in nutritional deficiencies going back to insufficient fertility of the soil.
Surely, the millions of health records of the inductees into our national defense will not be left lying idle in federal archives when they can be sorted out according to specific diseases, plotted as densities versus the soil fertility pattern, and possibly give suggestions for combating our failing health, which rests on the great fact that degeneration of the human body goes with the exploitation of the soil.
If the decay of teeth is indeed linked with the declining fertility of the soil, this concept of tooth troubles may well be a pattern to guide our thinking about other health troubles—not as calls for drugs and medicines, but for conservation in terms of a new motive, namely, better health via better nutrition from the ground up.
Figure. XIII. [Photo showing two sickly children standing on barren farmland, with the caption:] Human health goes with the soil and its fertility. (See original for image.)
By William A. Albrecht, AB, BS, MS, PhD, Department of Soils, College of Agriculture, University of Missouri. Reprinted from Annals of Dentistry, Vol. 8, No. 4, December 1947, by the Lee Foundation for Nutritional Research.
Note: Lee Foundation for Nutritional Research is a nonprofit, public-service institution, chartered to investigate and disseminate nutritional information. The attached publication is not literature or labeling for any product, nor shall it be employed as such by anyone. In accordance with the right of freedom of the press guaranteed to the Foundation by the First Amendment of the U.S. Constitution, the attached publication is issued and distributed for informational purposes.