is a regular steam service with Newhaven, and great numbers of Englishmen pass through D. on their route for Rouen and Paris. The exports are cottons, silks, woollens, fruits, &c., and the imports iron, steel, coal, and timber. D. has manufactures of lace, articles of ivory and bone, as also shipbuilding yards, sugar-refineries, distilleries, and sawmills. Its leading industry is, perhaps, in herring and cod fisheries, and in the management of the enormous beds of oysters in the vicinity. Pop. (1872) 20, 160. To the W. of D. lies the suburb of Pollet, remarkable for the entire contrast its inhabitants present to those of Upper Normandy in speech, dress, and manners, on which account they have been taken for the descendants of the Saxons who settled here in the times of the Merwings. D. is first. known historically in 1196, and subsequently became a flourishing French port. It rose to the height of its prosperity under François I. The ships which carried the first French colonists to Canada sailed hence. But the fortunes of D. sank with the revocation of the Edict of Nantes (1685), and the town was all but destroyed by the English and Dutch forces, July 17, 1694. It was rebuilt by royal command on the Peace of Ryswijk, and again bombarded by the English, 14th September 1803. The Germans, under Manteuffel, seized D. 9th December 1870.

Die-Sinking, the art of producing a design, usually incised, on a block of steel, called a die, which forms a matrix for the reproduction of a number of identical dies, used in striking medals, &c. The art is best displayed in the making of medals and coins. A piece of fine-grained steel is fashioned into a rough die-block, and is strengthened by a ring of iron to prevent its cracking. The rough die-block having been softened by annealing, and a smooth surface formed on it on the lathe, the die-sinker sketches and engraves in outline his design upon it. After delicate manipulation with differently shaped tools or gravers of many sizes, he produces a finished 'matrix.' While the die is being engraved, technically called 'roughed,' the diesinker takes frequent casts in clay or type-metal to test the correctness and progress of the work. A number of duplicate dies are prepared, as injury might result to the original from continual use in the press. The first step in the multiplication of dies is to harden the matrix by protecting the design with a charcoal paste, heating the steel to a bright cherry-red, and then exposing it to a falling stream of water. It is next cleaned, tempered by being raised to a certain temperature, and slowly cooled in oil or water, and 'lapped,' or polished. A piece of steel of the same quality as the die is now turned on the lathe to the form of a truncated cone, made quite smooth, and carefully annealed. The matrix being placed beneath a powerful press, the narrow end of the annealed piece of steel or punch' is placed upon it, and by a succession of light blows is sunk into the matrix till the design appears in perfect relief upon the punch. The blows require to be slight, as the punch is apt to crack, and softens after each blow. From the punch, which is strengthened with an iron collar and hardened, a series of impressions are obtained on soft steel, and from these, subsequently hardened, the medals or coins are struck by means of a press. All metals except tin have to be annealed after each blow in the press to prevent cracking. Dies for stamping notepaper, &c., and for fine kinds of metal ornaments, are prepared by the die-sinker. For inferior stamped metal ornaments the dies are chiefly cast, and afterwards touched up with a graver.

Di'es Incep'tus pro Comple'to Habe'tur, a legal maxim signifying that a day begun is a day ended. See COMPUTATION OF TIME.

Di'es I'ræ, the name given (from the opening words) to the great Latin hymn on the judgment-day-the crowning effort of mediæval piety in song. The modern world has nothing comparable to it in awe-stricken devotion and hallowed fear. The hymn has been ascribed to the General of the Minorite Order, Matthäus Aquasparta (died 1302), to Cardinal Frangipani (died 1294), to Malabranca, Bishop of Ostia (1274), to Bonaventura (q. v.), to St Bernard. (q. v.), and even to Gregory the Great (q. v.). But Luke Wadding, the learned historian of the Franciscan Order (Annales Minor., Lugd. 1625), assigns the authorship to Thomas of Celano, a native of the Abruzzi, and pupil and friend of St Francis of Assisi. Thomas died about the middle of Thomas died about the middle of the 13th c., and his name is first mentioned in connection with the poem about the end of the 14th c. There are three different 125

texts of the D. I.—(1) That of the Roman Missal, which is the one best known; (2) the Mantuan; (3) that given to the Cathedral of Zürich (about 1475) by Felix Malleolus (Ger. Hämmerlein), Provost of Solothurn and Chorherrn. The relative value of these texts is still the subject of critical discussion. The hymn itself first became part of the liturgy of the Church in the latter half of the 14th c. It has been repeatedly translated into German, English, and other tongues. Lisco, in his monographs on the D. I. and the Stabat Mater (Berl. 1840-43), enumerates sixty versions of the former, of which August Wilhelm von Schlegel's is probably the best. Crashaw, Macaulay, and Lord Lindsay are among those who have tried to render it into English. Di'esis, in music, a small interval (vibr. fraction, 128) occurring under the same circumstances as Diaschisma (q. v.).

Diest, a strongly fortified town in the province of S. Brabant, Belgium, 32 miles E.N. E. of Brussels, with manufactures of hosiery, beer, and gin. The Church of St Sulpitius is the only building of note. Pop. 7720.

Die'terichs, Joachim Friedrich Christian, a great veterinary surgeon, was born at Stendal, Prussia, 1st March 1792, entered the Veterinary College of Berlin as a bursar in 1813, and, after examination, was named in 1817 superior veterinary surgeon. He was sent to France at the expense of the Government to study stud-keeping and horse-breeding, and pursued the same study further in Würtemberg, Bavaria, Austria, and Hungary. On his return he occupied a chair in the Veterinary College of Berlin till 1823, was appointed to a post in the General Military School of Berlin in 1830, and appointed Professor in Ordinary in 1841. His works, which have been translated into various languages, are widely used in Germany. Among them are Handbuch der Veterinaer-Chirurgie (Berl. 1822, 6th ed. 1845); Ueber die Hulfbeschlagkunst (Berl. 1823); Handbuch der Speciellen Pathologie und Therapie für Landwirthe und Thierärzte (Berl. 1828, 3d ed. 1851); Handbuch der Geburtshilfe (Berl. 1845); Benennungen der einzelnen Regionen und Theile des äussern Pferdekörpers (Berl. 1853), &c.

Dietet'ics is that department of science which treats of food. The question of the kind of food best suited for man may be treated either theoretically or practically. Theoretically, food may be considered as consisting of various alimentary or proximate principles, each of which has specific physiological properties; or practically food may be regarded as composed of these collectively, in such proportions and in such physical states as fit the food for the maintenance of life. It is the practical aspect of the question of food which forms the subject of D. As an example of a natural food, take milk. It contains the following alimentary principles :-Nitrogenous matter (casein chiefly, with small quantities of other albumenoid matter), fatty matter or butter, a carbo-hydrate in the form of sugar of milk (lactine), and inorganic matter comprising salts and water. Here we find a combination of principles present, designed in the economy of nature for the purpose of sustaining life during an early period of mammalian existence.. An egg is another example of a compound food or material containing all the principles necessary for the development and growth of the body of the chick. It has also been shown by experiment that food containing a combination of principles is required to nourish the body of an animal. Thus gelatine, albumen, fibrine, and fat, taken separately, nourish animals for a very limited period, and in an incomplete manner. A truly nutritious food must contain a mixture of these, along with saline materials and water. In addition, a certain amount of sapidity or flavour is required to make the food palatable.

The nature of the food required by a healthy man is also affected by the exigencies of the climate in which he lives, and by his habits of life. Exercise and exposure to cold increase the demand for food, while a state of inactivity and a warm climate have usually the opposite effect. Again, dwellers in the Arctic regions consume an enormous quantity of the most efficient kind of heat-producing material-oleaginous matter, or fat,-while the inhabitants of the tropics live chiefly on vegetable products containing principles, such as starch, belonging to the carbo-hydrate group of bodies. In a temperate clime, we find men living more on a mixed diet. The following table by Moleschott may be regarded as representing the necessary combination of alimentary principles for maintaining health, in a 393

Water from 50 to 80 ounces. The 23 ounces of water-free material correspond to about 42 oz. of ordinary food.

For

a healthy average-sized man, doing a moderate amount of work, a sufficient diet of ordinary food would consist of about 8 oz. for breakfast, 6 oz. for luncheon, and 16 oz. for dinner-in all, 30 oz.

When we examine the dietaries of persons engaged in various ways, we find a correspondence between the work done and the food consumed, and here, as has been well said, there is a harmony between the dictates of experience and the suggestions of science. In order to ascertain the value of any dietary, the composition of the constituent articles requires to be known. The following table, compiled from Dr Letheby's Cantor Lectures on Food (1870, 1st ed. p. 6), represents the percentage composition

of several of the more common articles of diet :

As regards the effect of animal and vegetable food on the system, the following statements may be made:-(1) Animal food increases the amount of fibrin in the blood, renders the blood richer in red corpuscles, and produces firmness of muscle with an absence of superfluous fat. (2) Vegetable food increases the deposition of fat, is less stimulating than animal food, and appeases hunger for only a short time; otherwise its nutritious value, if capable of being digested, is quite as great.

Diet of Infants.-The proper food for an infant is the milk of the mother. Failing this, the nearest approach to the best food is the milk of another woman. A wet-nurse should be free from constitutional taint, and in a healthy condition. Her milk

* Understated.

To render cow's milk suitable for the infant, it is usually diluted with water and sweetened with sugar. Farinaceous food, consisting of bread, biscuit-powder, flour, rusks, &c., are not really suitable for infant life, although much used. Liebig's food for infants, derived from malt-flour, wheat-flour, cow's milk, bicarAs regards bonate of potash and water, is more suitable. practical dietetics and the food for invalids suffering from various diseases, see Dr Pavy's Treatise on Food and Dietetics (2d ed. Lond. 1875).

Die'trich of Bern, one of the characters in the old German epic the Niebelungen Lied (q. v.), and a favourite hero in German legend and song. In the Niebelungen Lied he is one of Etzel's (Attila's) chief vassals, and revenges the death of Siegfried by bringing Gunther, the Burgundian king, and Hagen, Siegfried's murderer, captive to Queen Chriemhilt. D. is only of secondary importance in the Niebelungen Lied, but is the central figure in a great cycle of Gothic tales. In the Heldenbuch, or Book of Heroes, written by Wolfram von Eschenbach and Heinrich von Ofterdingen, D. is represented as seeking adventures in a fairyland in the Tyrol, and as riding to Chriemhilt's rose-garden, and forcing the almost invulnerable Siegfried to hide beneath Chriemhilt's veil. Other sagas tell how D. was head of a band In the comof heroes, and was crowned Emperor of Rome. paratively late tale of D. and Sigenot, D. is shut up in a tower, and, like Ragnor Lodbrog, is attacked by snakes, but escapes. The story of D. and Ecke greatly resembles the Volsunga saga, and, according to some, can be connected with the Iliad. It paints D. as the bravest of all warriors, and as beloved by the beautiful Queen Seburk, whose pleading for D.'s life, according to Mr Cox (Mythology of the Aryan Nations, i. 305), symbolises the Dawn pleading for the life of the Sun. D. likewise appears King Hugh in France and Herne the Hunter in England. This in German legend as a ghostly midnight hunter, answering to

heroic and mythical D., or Thiderick, is identified with the great Ostrogothic conqueror Theodoric of Verona (q. v.). See Ludlow's Popular Epics of the Middle Ages.

Di'ets of Compearance, in the law of Scotland, are the days on which a party to a civil or criminal process is cited to appear in court. In criminal cases, the indictment, or Criminal Letters (q. v.), must be called on the precise day for which the accused is cited. See SUMMONS, INDICTMENT, INDUCIÆ LEGALES.

Diez, Friedrich Christian, an illustrious Romance scholar, was born at Giessen, March 15, 1794. After serving as a volunteer against Napoleon in 1813, and living as a private tutor at Utrecht, he went to Bonn in 1822, where he was appointed Professor of Modern Literature in 1830. He died 2d June 1876. D. was deeply versed in ancient and modern tongues, and by his two great works, Grammatik der Romanischen Sprachen (Bonn,

vols. 1836-42, new ed. 1850-60), and Etymologisches Wörter3d ed. 1870), which have been translated into English and buch der Roman. Sprachen (Bonn, 1853, 2d ed. 2 vols. 1861–62, French, founded the philology of the Romance languages. Among his other works are Die Poesie der Troubadours (1826), and Ueber die erste Portug. Kunst und Hofpoesie (1863).

Diff'erences, in heraldry, devices to indicate feudal alliance and dependency, but not blood-relationship. Another view is

that D. are used by the brothers and other descendants of a family after the death of their father, while marks of Cadency (q. v.) are employed during his lifetime. D. are effected in ways innumerable, by modifications of tincture and of all the charges-ordinaries, sub-ordinaries, and miscellaneous. Women cannot bear D.

18

The

Differences, Calculus of Finite, a branch of pure algebra, of the greatest importance in the discussion of series and questions of annuities, &c. The law which the successive terms of many series, at first sight very irregular, follow, is made quite evident by taking what are known as successive differences. following numbers give an example of thisSeries, First differences, 9 Second differences, 4 Third differences, The law is evident in the row of second D., while the fourth obviously vanish. It is apparent, then, that given any term and the corresponding differences, the other terms can be calculated. The two fundamental formulæ are-

40 58 82 113 152

27

13

18

24 31

39

5

6

7

8

I

I

I

I

series u1 + 2 + Uz +

x

x + I

x,

A2u AAU x Au, &c. For the proof and application of these, the reader is referred to De Morgan's Differential and Integral Calculus, and to Boole's Treatise on the C. of F. D.

Differen'tial, in music, is a third note produced when any two tones are sounded simultaneously. Its pitch is that corresponding to the difference between the number of vibrations of the two primaries. The D. has an important effect on the consonance of certain intervals. See CONSONANCE.

Differential Calculus. See CALCULus. Differential Equa'tions are equations in which differential coefficients of the variable quantities enter. They are divided

into two classes, ordinary and partial-the former having only one independent variable, the latter more than one. D. E. are also distinguished by their order and degree-the order being that of the highest differential coefficient present, and the degree corresponding to the highest power to which any differential coëffidy. cient is raised. Thus (224) + a dx. +xb is of the third order and second degree. If X, X1, X2, &c., be functions only

+ X2 dxn-1 is called a linear equation of the nth order, the dependent variable y and its derivatives being all of the first degree. Such equations are of great importance, being of very frequent occurrence in physical problems. The standard treatise on the subject is Boole's D. E.; while the chapter in De Morgan's Calculus is very complete and well worthy of study.

Differential Thermometer. See THERMOmeter. Diffraction, or according to Newton Inflexion, is an optical phenomenon which takes place when a ray of light passes very close to an opaque body. It was first observed by Grimaldi, and much studied by Newton, who supposed it to be due to a kind of molecular force subsisting between the opaque body and the light corpuscles. Let a narrow beam of sunlight, entering a darkened room, fall upon a plate which is perforated by an exceedingly small hole or slit. If the light transmitted through this minute aperture be received upon a white wall or sheet, the small light-spot will be surrounded by several concentric rings of coloured light with intermediate rings of darkness. The experiment may be varied so as to present most startling and beautiful phenomena, all of which, however, can be explained

upon the undulatory theory of light with a simplicity almost inconceivable. D. is, in fact, a case of Interference (q. v.). If a small opaque disc be interposed in a beam of sunlight, the shadow cast is found to have a small bright spot in the centre. This is another case of D.; and a general idea of the manner in which it is explained may be got from a consideration of the effect an obstacle has upon a wave travelling along the surface of a sheet of water. Where the crests of the two halves so formed meet, a larger wave will be produced, but where crest meets absence of that undulatory motion which constitutes light. The hollow, there will be no wave apparent; and darkness is the complete explanation requires the aid of higher mathematics, for which we refer to Fresnel's memoir before the Academy of Sciences Sur la D. de la Lumière (1826). A D.-grating is a transparent surface ruled with numerous lines, so close that they cannot be singly observed. By means of such an apparatus a series of most perfect spectra is obtained when a beam of sunlight, transmitted through it, is received upon a screen. These spectra are free from the objection which holds for prismatic spectra, that the violet portion is too much extended. Further, it is easily demonstrable, upon the principles of interference, that the distance of any portion of the spectrum from that point on the screen which is in the same line with the sunbeam and the centre of the grating, is proportional to the wave-length of the light at that part of the spectrum. This greatly increases the value of such gratings, which are, however, exceedingly scarce.

Diffusion, the gradual intermingling of two liquids or gases. If over a strong and coloured saline solution, such as sulphate of copper, or bichromate of potash, water be poured gently so as not to disturb the solution, the process of D. will become very apparent. For measuring the rate of D., however, this method is not sufficiently exact. Sir William Thomson employs but all intermediate between those of the two liquids. As D. goes a number of glass beads, whose specific gravities are different, on the beads gradually separate, and indicate by their positions the specific gravity at any depth of the solution. Another method adopted by the same physicist is to measure the refractive indices of the various layers of the diffusing liquids. There are many pairs of liquids, such as water and oil, which do not mix, and therefore do not diffuse, and there are others in which the D. is only partial, the final result being the lighter liquid mixed with a small proportion of the heavier floating upon, and distinctly marked off from, the heavier liquid, mixed with a small proportion of the lighter. This is the case with ether and water. marked by Priestley. Graham, who investigated the phenomenon Every gas is capable of D. into every other gas-a fact first rethoroughly, has shown that the rate at which the D. of any substance goes on is proportional to the rate of variation of the strength of that substance in the fluid as we pass along in the direction of the D.; exactly the law which holds for conduction of heat and electricity. He also deduced from his experiments that the rates of D. of two gases are inversely proportional to the square roots of their densities--the lightest diffusing most rapidly. If a porous solid be intercepted between the two gases, D. takes place, according to Graham, in the same way that it would have done if there had been no septum present; Bunsen, however, regards the phenomenon as dependent upon capillarity, and doubts the truth of Graham's law of densities. There is another class of cases, differing from the last in the fact that the diaphragm is not in the ordinary sense porous. Thus, if a soapbubble be blown with carbonic acid bubble be blown with carbonic acid gas, the gas is continually passing through-being absorbed on the interior surface, passed in a state of solution through the film, and given off at the exterior surface. Hydrogen and other gases behave similarly with respect to caoutchouc; but their rates of passage have no connection with those of ordinary D., being rather a chemical than a mechanical action.

Graham distinguished what he called colloid and crystolloid substances; the former being capable of uniting temporarily and loosely in various proportions with other substances, the latter always combining in definite proportions. Glue is a colloid body, forming a jelly with various proportions of water; salts are crystalloïd. They are easily distinguished by the difficulty with which all colloïd bodies diffuse through a porous solid, crystalloïds diffusing with ease. If a colloïd substance be combined with some liquid or crystalloïd solution in different proportions throughout its mass, D. takes place through the colloïd body till

395

the structure is homogeneous—an interesting analogy to the tendency which an unequally heated body has to come to a uniform temperature. It is on this theory that Graham explains the passage of hydrogen through iron and palladium at a high temperature, the metals acting, with respect to the gas, as colloïd substances. See Graham's Memoirs in the Philosophical Transactions prior to 1851, Graham's Chemistry, Bunsen's Gasometry, translated by Roscoe, and Clerk Maxwell's Theory of Heat.

Digamma, a letter once occupying the sixth place in the Greek alphabet, which gradually fell into entire disuse. It was called D., i.e., double gamma, from its resemblance to two gammas placed one on the other, ff F. The D. existed in the time of Homer, but is not found written in any extant copy. In pronunciation it answered to the English v. The manner of its disappearance may be illustrated by a comparison of the Greek aiōn, oinos, with the Latin ævum, vinum.

Dig'by, a seaport in the Dominion of Canada, province of Nova Scotia, on the Bay of Fundy. It has an active industry in the curing of pilchards, which are prized on account of their flavour, and are known as Digbies in the fish trade. There are also valuable herring and mackerel fisheries, and some shipbuilding and lumbering. Pop. (1871) 1300.

Digby, Sir Kenelme, the son of Sir Everard D., one of the men who suffered for participation in the Gunpowder Plot, was born in 1603, at Gothurst, in Buckinghamshire. He distinguished himself at Oxford, and after two years' travel on the Continent was knighted by James I. Charles I. appointed him to numerous offices, and in 1628 he sailed with a squadron to the Levant, where he defeated the Venetians. He also fought with the Algerines. Originally a Protestant, D. became, in 1636, a Roman Catholic. When the civil war commenced he was imprisoned as a Royalist, but was released in 1643. For a long time he resided and studied in France, returning to England in 1661, and dying there, 11th June 1665. D., who was a learned man, and an adherent of what is known as 'the corpuscular philothe corpuscular philosophy,' is the author of numerous works, including A Treatise of the Nature of Bodies, an interpretation of The Twenty-second Stanza in the Second Book of Spenser's Faerie Queene, and Two Treatises on the Nature of Bodies and of Man's Soule. His private memoirs were published in 1827.

Di'gest, the name given to the Pandects of the civil or Roman law, as containing Legalia præcepta excellenter digesta. See CODE. Diges'ter, Papin's, a strong metallic vessel, tightly fitted with a lid, and provided with a safety valve. It is used for subjecting bodies to a higher temperature than could be obtained by merely boiling water in the usual way; for the steam, being unable to escape, increases the pressure upon the water, the boiling-point of which is consequently raised.

Digestion. This is a term given to the processes by which the food is changed into a condition suitable for being absorbed into the blood-vessels or by the lacteals. During the course of D. the food is changed physically and chemically; it passes through various organs, and it is acted on by various juices. In the mouth the food is divided and comminuted by the teeth. It is mixed, at the same time, with the various fluids which compose the saliva. Having been reduced to a pulpy mass, it is, by the action of the tongue, passed backwards into the pharynx, and by the successive contractions of the muscles of the pharynx it is propelled into the oesophagus. This tube leads from the pharynx into the stomach, which is a receptacle for the food, and the cavity in which the chief digestive processes occur. In the stomach the food is subjected to three actions :-(1) To a triturat:) To a triturating movement, effected by the contractions of the muscular walls of the stomach, by which it is thoroughly mixed with the juice | secreted by glands in the lining membrane of that organ, called the gastric juice; (2) to the chemical action of the gastric juice; and (3) to the influence of a temperature of about 100° F. The food is thus further reduced into a pultaceous or gruel-like mass called chyme, and as it is partly liquified, portions successively pass into the small intestine (see STOMACH), while the larger masses are left behind in the stomach to be further acted upon. In the small intestine (see INTESTINE), which is about 15 to 20 feet in length, the chyme is mixed, as it is slowly propelled along the bowel, with-(1) The intestinal juice; (2) the bile; and (3) the pancreatic juice. By these juices certain of the constituents of the food are further acted upon, and the alimentary

matters, thus liquified and prepared, are gradually absorbed by the blood-vessels of the intestinal mucous membrane and by the lacteals, and become chyle. The indigestible portion of the food is passed by the muscular action of the walls of the small intestine (see PERISTALTIC ACTION) into the large intestine, from which, with certain refuse or excrementitious substances, it is expelled by the act of Defecation (q. v.).

The action of the various digestive fluids on the proximate constituents of food may here be briefly summarised, while reference is made, as to the structure of the various organs and as to the composition of the various fluids, to the following headings:-MOUTH, PHARYNX, DEGLUTITION, ESOPHAGUS, STOMACH, GASTRIC JUICE, INTESTINE, LIVER, SALIVA, and PANCREAS. Five digestive fluids act on the food:-

(1.) Saliva, which converts starch into sugar, and assists in Deglutition or Swallowing (q. v.).

(2.) Gastric juice, which acts on the albuminous matters, converting them into Peptones (q. v.), or soluble modifications of

albumen.

(3.) Bile, which separates the refuse from the nutritious matter caused by the gastric juice, aids in the absorption of fat by of the chyme, neutralises any excessive acidity of the chyme covering the surface of the mucous membrane with an alkaline fluid, stimulates the peristaltic action of the bowels, and arrests putrefactive changes. See BILE, LIVER.

(4.) Pancreatic juice, which emulsionises fatty matter, splits up certain fats into glycerine and the corresponding fatty acid, converts starchy matter into sugar, and converts peptones into two substances called Leucine and Tyrosine (q. v.), which are then absorbed and taken to the liver.

(5.) Intestinal juice, which, so far as is known, combines the actions of all the other juices, and acts on the albuminous, starchy, and fatty principles.

The conditions favourable for good D. in the stomach are— (1) A temperature of about 100° F.; (2) constant movement of the walls, which brings in succession every part of the food in contact with the mucous membrane and gastric juice; (3) the removal of such portions as have been fully digested, so that what remains undigested may be brought more completely into contact with the solvent fluid; and (4) a state of softness and minute division of the aliment.

According to the celebrated experiments of Dr Beaumont upon St Martin, a Canadian, who, on 6th June 1822, met with a severe gunshot injury, the result of which was a permanent fistula or opening into the stomach, the rapidity of D. varies according as the food is more minutely divided, whereby the extent of surface with which the gastric fluid can come in contact with it is proportionally increased. Liquid substances are for the most part absorbed by the vessels of the stomach at once, and any solid matters suspended in the liquid, as in soup, are concentrated into a thicker material before the gastric juice acts upon them. A full meal, consisting of animal and vegetable substances, may be converted into chyme in about an hour, and the stomach may be left empty in two and a half. Rice and tripe, in St Martin's case, were digested in about 1 hour; eggs, salmon, trout, vension, and apples, in 1 hours; tapioca, barley, milk, liver, and white fish, in 2 hours; turkey, lamb, and pork, in 2 hours; beef, mutton, and fowls, in 3 hours; and veal in about 4 hours. The following circumstances no doubt also affect D. :-(1) The quantity of food taken-the stomach should be moderately filled, but not distended; (2) the time which has elapsed since the last meal, which should be always long enough for the food of one meal to have completely left the stomach before more is introduced; (3) the amount of exercise previous and subsequent to a meal, gentle exercise being favourable and over-exertion injurious to D.; (4) the state of mind, tranquillity of temper being usually essential to quick and due D.; (5) the bodily health; (6) the state of the weather; (7) the period of life, D. being more active in the young than in the old.

The quantity of digestive fluids secreted daily, according to the estimates of Bidder and Schmidt, which are probably (with the exception of the last two) at least 25 per cent. too high, is, in pounds avoirdupois :-Saliva, 3'5; bile, 3'5; gastric juice, 14'1; pancreatic juice, 0'44; intestinal, 0 ̊44.

The survey of the digestive functions throughout the animal series leads us to contemplate very wide variations in the form and complexity of the assimilative apparatus. In the Protozoa (q. v.), or lowest animals, the bodies of which are com

THE STOMACH LAID OPEN BEHIND.

a, the oesophagus; b, the cardiac dilatation; c, the lesser curvature; d, the pylorus; e, the biliary duct; f, the gall-bladder; g, the pancreatic duct, opening in common with the cystic duct opposite, h h, i, the duodenum.

substance. This substance, therefore, constituting of itself a living being, assumes the functions of a digestive system. Even in these lower animals, an essential difference from plants may be perceived in the process of D., in that they receive their nutritive matters within their bodies, and digest them internally, whilst in plants the process of nutrition goes on in the external surfaces and outer tissues of the organisms. Some of the protozoa (e.g., Gregarine), and some more highly organised animals also (e.g., tapeworms), live by simple imbibition-that is, by simply absorbing the fluids on which they subsist. And in such forms no distinct or specialised mouth, stomach, or other digestive apparatus exists. In none of the protozoa, except in the Infusorial (q. v.) animalcules, does a mouth exist; and in the latter no digestive system is specialised, food being digested by the protoplasm of which the body is composed. In the Coelenterate animals (represented by the hydræ, sea-anemones, zoophytes, corals, &c.), a stomach-sac may be wanting, as in all Hydrozoa, and food is digested simply within the general cavity of the body. But in the sea-anemones and other actinozoa a distinct stomach-sac is specialised, although this latter structure is open inferiorly, and communicates thus with the body-cavity. Tentacles are also now found, by means of which the food is drawn towards the mouth-opening, which is always developed. In Annuloida or echinozoal animals (such as sea-urchins, starfishes, sea-cucumbers, &c.), a perfect digestive system is usually to be found, although, as in the tapeworms, already noticed, a digestive apparatus may be wanting, possibly in consequence of their degraded condition as internal parasites. In Annulosa (such as worms) the digestive system is of tolerably perfect structure, and when we advance to the higher members of the latter sub-kingdom (such as insects, spiders, crustacea, &c.), we find not only a perfect digestive apparatus, but many supplementary organs in addition. In insects, a crop and gizzard, stomach, intestine, biliary or liver tubes are found, with a heart and blood-vessels for the circulation of the nutritive fluid. In higher crustacea, such as lobsters, &c., the digestive structures become still further specialised, the liver especially becoming better developed. In Mollusca (such as cuttlefishes, snails, oysters, &c.), salivary glands, teeth-like structures for the trituration of the food, and a large liver exist. In Vertebrata, and among fishes representing the lowest group of the class, the digestive system may include not only a mouth, teeth, stomach, and intestine, but also a liver, pancreas or sweetbread, and other structures. In Amphibia (q. v.) a spleen is also present, and in reptiles some further specialisation exists. In birds no teeth are developed; but a gullet, crop, gizzard, and proventriculus or true stomach, together with an intestine, intestinal cæca, liver, pancreas, spleen, and other glands are found.

It may be noted that vertebrates differ from all lower animals

in possessing a distinctly developed lacteal or Absorbent System, that is, a special system of vessels, the function of which is to receive the products of D. from the digestive canal and transfer them to the blood system, where they mingle with the current of the circulation and thus repair the bodily waste. And as a rule of the most universal character throughout the entire animal series, it may also be remembered that the digestive system of an animal feeding upon plants or vegetable food is longer and of more complicated nature than that of an animal feeding upon flesh. The contrast between the digestive systems of a grain-eating and a flesh-eating bird in this respect is seen to be very marked; and the contrast is equally well observed in the difference between the digestive system of the larval frog or tadpole and that of the carnivorous adult frog.

In mammalia broad variations in the form and complexity of the digestive systems are noticeable. In some the system is comparatively simple, whilst in others as in some marsupials, but most notably in the case of the ruminants (sheep, oxen, &c.), or those that chew the cud'-the stomach evinces a highly complex nature. The structure of the ruminant digestive system will be noted under the head of Ruminant (q. v.) and Rumination (q. v.). Variations exist in the mammalian digestive organs chiefly in the relative length of the intestinal canal, in the nature and number of the teeth, in the development of the tongue and other appendages, and in the glands connected with the system.

Dig'it (Lat. digitus, 'the finger'), in arithmetic, the name given to each of the symbols, o, 1, 2, 3, &c., to 9; in astronomy, the twelfth part of the diameter of the sun or moon. In anatomy the name is applied to the fingers and toes of the Vertebrata.

Digital'ine is the active principle of the common foxglove (Digitalis purpurea). It is colourless, crystalline, and sparingly soluble in water; dissolves more readily in alcohol and ether, and is very bitter and poisonous. Considerable doubt exists as to its true chemical composition. It belongs, however, to the class of bodies called Glucosides (q. v.), for when boiled with dilute acids it takes up water and splits into Glucose (q. v.) and other products. D. is a valuable medicine,

It

Digitalis, a genus of plants of the natural order Scrophulariacea. They are biennials or perennials, with erect stems and large showy flowers in long one-sided racemes. They are natives chiefly of Europe and the N. of Asia. D. is often cultivated in gardens, especially the yellow D. grandiflora. Only one species is native in Britain—D. purpurea, the common purple foxglove, It grows from 2 to 4 feet high, with beautiful flowers spotted inside. occurs in dry hilly places, roadsides, and plantations. It abounds in Western and Central Europe, and extends as far as Scandinavia. The leaves of D. purpurea are used in medicine. They are collected from wild plants in Britain when about two-thirds of the flowers are expanded. They are used as powder tincture and infusion. In large doses D. is an irritant poison, and in small doses it depresses the heart's action, and increases the flow of urine. cine in certain kinds of heart-disease, and very specially in dropsies depending on heart-disease; but being cumulative in its action, it should be administered with great caution. Its active principle is Digitaline (q. v.).

Digita'ria. See MILLET.

Digitalis purpurea.

It is a valuable medi

Digitigra'da ('toe-walkers'), the name applied to that section of the mammalian order of Carnivora of which the included members walk on the tips of their toes, the heel being raised from off the ground. Examples of such forms are found in the Felida (tigers, lions, cats), Canide (dogs, wolves, &c.), &c. Some forms (e.g., Mustelide or weasels) are termed semi-plantigrada, since they apply only part of the sole to the ground in walking; whilst the bears are wholly Plantigrade, and apply the entire sole of the foot to the ground.

Digne, the capital of the department Basses-Alpes, in a wild mountain gorge on the left bank of the Bléone, 45 miles N. E. of