NUTRITION . The See also:

• PHYSIOLOGY (from Gr. 4 i s, nature, and koyos, discourse)

1. CHEMISTRY OF DIGESTION The essential step which prepares the See also:

• ORDINARY (med. Lat. ordinarius, Fr. ordinaire)

1. Male See also:

• FLOWER (Lat. flos, floris; Fr. fleur)
• FLOWER, SIB

The starches or polysaccharides are broken down, first of all to the See also:

• SIMPLE

The amount of solids present is extremely small, about o•3 %. They consist of protein, nucleic acid, lecithin and inorganic salts, in addition to the more important constituents, the enzymes and hydrochloric acid. The amount of hydrochloric acid present in the juice varies with the period of digestion. In man the maximum acid concentration is about 0•2 %. The acid exists in the stomach in two forms as See also:

• FREE

In 1897, however, E. See also:

• BUCHNER, FRIEDRICH KARL CHRISTIAN LUDWIG (1824-1899)

Ferments which bring about the breakdown of proteins are with-out influence on fats and carbohydrates; those which decompose fats leave proteins and carbohydrates untouched, and so on. The chemical composition of enzymes is unknown. It has been assumed that they are protein in nature, but this is mainly because it has been found that when they are extracted from tissues they are apparently in See also:

• COMBINATION (Lat. combinare, to combine)

In the See also:

• CASE
• CASE, JOHN (d. 1600)

Certain oxydases, catalases and de-amidizing enzymes are found in the tissues generally and See also:

• PLAY

See also:

• MILK (0. Eng. meoluc; from a common Indo-European root, cf. Lat. mulgere, Gr. ?t dXyetv)

That lime salts are absolutely essential for this process of clotting has been shown by the fact that, if they are removed by precipitation as by oxalates, no clotting will take place even after the addition of a large amount of active rennin. Immediate clotting takes place, however, when the necessary lime salts are restored. Many observers now hold that this rennet action is not the See also:

• PROPERTY

There is no doubt that fats present in fine emulsion can be de-composed in the stomach. The action proceeds in a medium which is slightly acid or neutral, being entirely prevented by the presence of strong acids and alkalis. Many workers believe this gastrolipase to be of pancreatic or intestinal origin, and suppose that it gains entrance to the stomach by a reflux flow through the pylorus. See also:

• EVIDENCE (Lat. evidentia, evideri, to appear clearly)

The secretion obtained from a See also:

• FISTULA (Lat. for a pipe or tube)

Its effect is much more energetic than that of pepsin, so that the protein See also:

• MOLECULE (from mod. Lat. molecula, the diminutive of moles, a mass)

As already ;mentioned, the See also:

• MAIN (from the Aryan root which appears in " may " and " might," and Lat. magnus, great)
• MAIN (Lat. Moenus)

This process is said to take place in two stages: (i) the The character and properties of the products formed in such digestion depend on the nature of the protein acted upon. As will be seen from the following table these proteins vary fairly widely in the proportion of amino acids which they contain. moo Grammes Protein yielded Caseinogen. Gelatine. Globine Elastine. from Oxy- haemoglobine. Glycocoll 16.5 25.75 Alanine . 0.9 o•8 4'19 6.58 Leucine . I0•5 2•I 29.04 21.38 aProline . . 3'1 5.2 2.34 1.74 Phenyalanine 3.2 0.4 4'24 3'89 Glutamic acid 10.7 o•88 1.73 0.76 Aspartic acid 1.2 0.56 4'43 Cystine . . 0.065 .. 0.31 Serine 0.23 ..

0.56 Oxyproline . 0.25 3'0 1'04 Tyrosine 4'5 I'33 0.34 Lysine . . 5.8o 2.75 4'28 Histidine 2.59 0.40 10.96 .. Arginine . . 4.84 7.62 5.42 0.3 Tryptophane 1.5 .. Present Whether any of the polypeptides found in digestion are further broken down in the course of normal pancreatic digestion is a See also:

• MOOT

It deals with all the starchy food which has escaped con-version into the simple sugars by the ptyalin. c. Lipase.-Most of this ferment, if not all, is apparently secreted in the form of a zymogen. There is evidence that the bile iS the activating agent here, just as the enterokinase acts in the case of trypsin. Lipase can act in any medium acid. neutral, and alkaline, and both on emulsified and non-emulsified fats. It converts the fats by a process of hydrolysis into fatty acids and glycerin. Kastle and I,oevenhart found that not only can this enzyme break up fats into their components, but that it also has the power to act in the See also:

• REVERSE

b. Intestinal Digestion.-By this is meant the other digestive processes which go on in the intestine under the action of the secretion of Lieberkiihn's follicles-the succus entericus. This is a yellowish, often opalescent, strongly alkaline fluid. The alkalinity is due to the presence of sodium carbonate. It contains a small amount of protein, See also:

• SHED

Another ferment, arginase, has been isolated from the intestinal mucous membrane by A. Kossel and H. D. Dakin, which splits the diamino acid arginin into See also:

• UREA, or CARBAMIDE, CO(NH2)2

Any digestion which does take place is probably either bacterial in origin, or due to ferments which have originated in the lower end of the small intestine, and which have been carried down. 5. Bile.-This fluid, in all probability, has little See also:

• DIRECT

It contains in addition to a nucleo-albumin, derived mainly from the bile passages and gall bladder, bile acids, bile See also:

• PIGMENTS (Lat. pigmentum, from pingere, to paint)

The taking of food increases the flow of bile, the amount of the increase depending to a certain extent on the nature of the food. A protein meal has been found to have the greatest effect and a carbohydrate one the least. The entry of the acid chyme into the duodenum is the stimulus which brings about the ejection of the bile. Pressure on the liver also seems to cause a flow (see See also:

• SECTION
• SECTION (Lat. sectio, cutting, secare, to cut)

Of the inorganic constituents iron is probably for the most part excreted into the large intestine. It is, however, very difficult to come to any definite conclusion as to what is unabsorbed material and what excreted. H. THE MODE OF FORMATION OF THE DIGESTIVE SECRETIONS r. Salivary Glands.-The secretion from the various glands is generally evoked by See also:

• NERVOUS

Further, if the circulation be cut off from the gland the stimulation of the chorda tympani may cause a temporary flow of saliva. The parotid gland is supplied by the auriculo-temporal nerve which receives its secreting fibres from the glossopharyngeal. Stimulation of these fibres brings about an abundant watery secretion poor in solids. Stimulation of the sympathetic fibres See also:

• SYSTEM

There may be certain substances either present,in the food or See also:

• DEVELOPED

The active substance present in this extract is known as "secretin," and is supposed to be formed under natural conditions by the action of the acid chyme on a prosecretin. This secretin is not of the ordinary zymin nature, as it is not destroyed by boiling and is soluble in alcohol. The secretin when formed must be absorbed into the blood and then carried See also:

• ROUND (O. Fr. rond, Lat. rotundus, the Fr. is the source also of Du. rond; Ger., Swed., Dan. and Nor. rond)

The food is now passed on into the See also:

• OESOPHAGUS (Gr. o'lvca=I will carry, and r/)ayeiv, to eat)

In this connexion it must be remembered, of course, that the food is not lying loose in a See also:

• SACK

Under normal conditions they begin at the pylorus and passing down-wards carry the intestinal contents onwards. The normal movement progresses slowly, although under abnormal conditions peristaltic waves may become extremely violent and rapid, and may indeed run over the whole length of the intestine within a See also:

• MINUTE
• MINUTE (Lat. minutes, small; minuere, to make less)

Starling, although they continue and indeed may become more energetic after section of the extrinsic nerves, are prevented by the application of nicotine and See also:

• COCAINE, C17H21NO4

The act of defaecation normally is partly voluntary and partly involuntary. The voluntary part consists in the contraction of the abdominal muscles, the closure of the glottis, and the relaxation of the external sphincter and of the levator See also:

• ANI (anc. Abnicum)

Water passes rapidly through the stomach and is practically unabsorbed. Salts are apparently absorbed in a limited amount from their watery solution, the extent of absorption depending to some extent on the concentration of the solution. Sugar is also absorbed to a small extent from its solutions, the greater the concentration the greater being the amount of sugar taken up. Alcohol is readily absorbed from the stomach. A small amount of the products of protein digestion may be absorbed: There is no evidence that fats are absorbed under any conditions in the stomach. Intestine,.—The greatest absorption of the foods takes place in the intestine, especially in the small intestine. It has been shown that over 85% of the protein has disappeared before the lower end of the small intestine is reached. How does the absorption take place? There are two channels for the removal of the material from the intestine: (r) the blood capillaries spread in the villi, and (2) the lacteals also present in the villi. The foods may reach the blood direct or through the various See also:

• LYMPH

Can absorption be explained by the ordinary laws of See also:

• DIFFUSION (from the Lat. diffundere; dis-, asunder, and fundere, to pour out)

F. Rohmann found that the absorption of the disaccharides is dependent on the invert ferment action, and not upon their osmotic characters. E. Weinland too has shown that if lactose be put into a lactase-free intestine, no absorption takes place, the lactose gradually disappearing under bacterial action, whereas when the ferment lactase is present See also:

• GLUCOSE (from Gr. - twais, sweet)

As already mentioned, the fat is removed by the lacteals from the cells to the thoracic duct, and then to the general circulation. A small amount of the fat may pass into the body via the blood, but this is practically all retained by the liver. The amount of fat absorbed depends a good deal on the nature of the fat, especially with reference to its melting-point, fats of low melting-point being most readily taken up. Protein.—The older workers held that the protein was absorbed in the form of proteose and peptone. In support of this it was stated that both proteoses and peptones could be detected in the blood stream. The result of the most recent work tends to show that the material is absorbed in the form of the amino acids either simple or in complex groups, the polypeptides, and that if proteoses or peptones be absorbed they are attacked by the See also:

• INTRA

V. METABOLISM In all living matter there is a See also:

• CONSTANT, BENJAMIN (1845-1902)

Fischer we are no longer in this position. Gradually our knowledge is being broadened by actual facts obtained by direct experiment, or by inference from previous experiments. But it is still far from complete. It is only possible to outline what is at present known about the part played by the different food constituents in metabolism. Proteins.—Since these alone contain the nitrogen necessary for the building up and repair of the tissues they are essential and will be dealt with first. In considering the digestion of proteins it was shown that in all probability all protein food was reduced in the intestine to comparatively simple crystalline bodies. O. Loewi has shown that an animal can be maintained in health without loss of weight by feeding it on a diet consisting of amino acids obtained by prolonged pancreatic digestion in place of proteins. In addition to these acids abundant carbohydrates and fats were given. It has since been shown that the presence of carbohydrate a certain amount of is absolutely essential before utilization of the amino acids can take place. Further, it has been demonstrated that only a mere fraction of the See also:

• TOTAL

What then does the body gain by breaking down food material to such simple bodies, if it is immediately to be resynthesized ? This complete breakdown appears to be to facilitate rebuilding. The protein in the protoplasm of each animal is characteristic and to build up these different proteins the material must be separated into its nuclei. An experiment carried out by E. Abderhalden shows this very clearly. A protein gliadin absolutely different in constitution from the proteins of blood plasma was fed to an animal from which much of its blood had been removed, so that an active reformationhad to take place. The question to be solved was whether by feeding with a protein so absolutely different in constitution the nature of the freshly forming serum protein could be radically changed. But the newly-formed serum was found to be exactly the same in constitution as the old. The tissues had selected simply those nuclei of the gliadin which were required and had rejected the others. In addition to this breakdown of protein in the intestine, another See also:

• FACTOR (from Lat. facere, to make or do)

Thus it would seem probable that any excess of the amino acids formed does not reach the liver as such but denitrified as members of the fatty acid series. The ammonia split off is also conveyed to the liver and is excreted for the most part as urea, within the first few hours after a protein meal. Thus, in all probability very See also:

• EARLY
• EARLY, JUBAL ANDERSON (1816-1894)

This glycogen is an insoluble polysaccharide, and is only utilized according to the requirements of the body, especially during muscular exertion. Carbohydrates, when taken in in excess, are also stored in the tissues in the form of fat. This was demonstrated by the feeding experiments of See also:

• LAWES, HENRY (1595-1662)
• LAWES, SIR JOHN BENNET, BART

If in larger amount they are stored as fat, to serve as a reserve in case of need, in the body tissues. Like the carbohydrates they serve as the See also:

• SOURCES

Muscular Work.—The muscular tissue plays the most important part in general metabolism. Not only is muscle the most abundant tissue present, but it is constantly active and is the great energy-liberating See also:

• MACHINE
• MACHINE (through Fr. from Lat. form machina of Gr. µnxavil)

The medullary part of these organs is developed from the sympathetic part of the nervous system, and adrenalin acts as a stimulant to the terminations of the sympathetic nerves which See also:

• SPRING (from " to spring," " to leap or jump up," " burst out," O. Eng., springau, a common Teut. word, cf. Ger. springer, possibly allied to Gr. QnrFpxecOac, to move rapidly)

The well-known effects of removal of the ovaries or testes on the development and character of an animal is due to the See also:

• ABSENCE (Lat. absentia)

Other factors, besides these already dealt with, play a part in modifying the various metabolic processes, as age, temperature, See also:

• CLIMATE

The urine is the main channel of excretion for the nitrogenous waste products. CO2, arising for the most part from the metabolism of carbohydrates and fats, is excreted mainly through the lungs. Water is excreted by the lungs, the kidneys and the skin. So far no entirely satisfactory explanation has been given of how a fluid like urine, having an acid reaction and containing about one See also:

• HUNDRED

The ammonia is utilized by the body to neutralize acids which arise during the various metabolic processes. Pursns (uric acid, xanthin, hypoxanthin, &c.) are all members of a series which have as their See also:

• COMMON

. . 14.8-18.2 gyms. per day 4.8- 8•o grms. per day Urea nitrogen 86.3-89.4 % of total 62.0-80.4 % of total Ammonia nitrogen 3'3- 5'1% „ 4'2-11' 7 % Creatinin nitrogen 3.2- 4.5 % ++ 5'5-II.1 % Uric acid nitrogen o•5- 1.0 % „ 1.2- 2.4 Undetermined nitrogen 2.7- 5.3 % „ 4.8-14.6 % with the See also:

• SPECIES

Hence it would seem to be derived from the creatin of muscle, a substance which is very readily changed into creatinin outside the body. In the body the conversion of creatin into creatinin seems to be strictly limited, and hence when creatin is taken in flesh in the food it tends to appear as such in the urine. It would seem that it is either in great part decomposed in the body into what we do not at present know or that, as suggested by Folin, it may be used as a specialized food. Whatever its source, after urea and ammonia it is one of the most important nitrogenous substances excreted, the daily excretion being about 1.5 grms. The See also:

• SULPHUR

The lungs are the important channel of excretion for the waste product of carbon metabolism CO2 (see See also:

• RESPIRATORY