An intermediate textbook of physiological chemistry with experiments

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Preface

My aim in writing this book has been to prepare an intermediate text which would cover the general field of physiological chemistry in such a way as to give students a familiarity with compounds important from a biochemical viewpoint, and to acquaint them with the fundamental processes which go on in the animal body. I have attempted to avoid confusing the beginner with lengthy discussions of debated points, bnt to set forth as clearly as possible the present status of our knowledge. The material is so chosen that the book may be used for intermediate classes, or for advanced work if supplemented by lectures.

The appended laboratory work has been drawn from the manual in use in my classes for the last five years. Much of the material baa, of course, been drawn from other manuals.

As the book is not intended to be an advanced text, the micro methods for the analysis of urine have not been included.

I wish to acknowledge suggestions and corrections in the laboratory directions from various colleagues, particularly Dr. F. B. Kingsbury. I wish also to express my thanks to Dr. W. H. Hunter, who kindly volunteered to read the manuscript of the theoretical portion,

C. J. V, Pettibone.

Minneapolis, Minn.

Contents

CHAPTEE I

IKTEODUCTOEY

Object and Importance of Physiological Chemistry, 17; Protoplasm, 18; Hat«riat Basea, 19.

CHAPTER II Elements, Inoroanic Materials, Water

Elements Pound in the Body, 21 ; Importance Not Detennined by Amount Present, 21; Carbon, Hydrogen, Oxygen, Nitrogen, Sulphur, and Fhosphorua, 22; Sodium, Potassium, Calcium, MagueBium, and Iron, 24; Chlorine, Iodine, Fluorine, Etc., 26; water, 26.

CIIAPTEK III

Carboiitdkatbs

Composition, Ocourronce, General Function, 27; Structure of the Carbohydrates, 27; Optical Activity, 28; Classification of Cnrbohydratea, 34; Origin and Synthesis, 35; Interoon version of Carbohydrates, 37; Combination of Caibohydratea with One Another, and with Other Substances, 33) Behavior with Strong Alkalies, 3S; Behavior with Acids, 39; Oxidation of Carbohydrates, 40; Beductiou of Carbohydrates, 42; Formation of Osazones, 43; The Molisch Test, 44; Formontation — Enzymes,. 44; Nomenclature and ClaSBification, 46; Specific Nature, 47; Influence of Temperature, 47; Effect of Chemical Reaction, 47; Reversibility, 48; Active and Inactive Form, 48; Action Retarded by Products, 48; Progressive Action, 48; Summary, 49; Individual Groups of Cafbohyd rates, 49; Pentoses, 49; Absorption Spectra, 50; Hexoses. C,H„0„ 51; Glucose, 51; Fructose. (Levulose, Fruit Sugar), 52; d-Oalactose, 52; Amino Sugars, 53; d-Glucuronic Acid, 53; Disaccharides, 54; Saccharose, (Sucrose, Cane Sugar), 54; Lactose, 56; Maltose, 57; Polysaccharides, 57; Starch (C,H„0,)j,., 58; Dextrins, 59; Inulin, 59; Gums and Mucilages, 59; Cellulose, 59; Glycogen, 60; Qlucosides, 61.

12 CONTENTS

CHAPTEB rV Fats, Fhosphatiss, am Allied Substances Distribution and Importance, 62; CompoBltion and Structure, 62; Qenenl Propertiea, 64 ; Emulaiflcation, 64 ; Baponificatioo, 65 ; Bancid Fats, 6S ; Detection and Identifleation, 66; Import«nt Fat«, 68; Lecithin and Cholesterol, 6S; Lecithin, 69; Choleaterol, 70.

CHAPTEB V

PE0TI3NS Introductory, 72; Elementarj CompOHition, 72; ClaBsification, 73; Preparation of Proteina from Mat«ria]s in Which They Occur, 74; Molecular Weight, 75; Hydrolysis, 75; Amino Acids Obtained by Hydrolyzing Protein, 76; General Properties and B«actionB of Amino Acids, 79; Qeneral Protein Beactions, 82; Color Tests, 82; Precipitation Reactions, 84; Colloids, 84; Classification and Properties of Colloids, 84; Tyndall's Phenomenon, 86; Electrical Properties of Colloids, 86; Methods of Precipitating Colloids, 86; Structure of the Protein Molecule, 89; Putrefaction of Proteins, 93 ; Individual Groups, Simple Proteins, 95 ; Albumins, 95 ; Olobulius, 95 J Olutelins, 96; Prolamines, S6; Albuminoids, 96; Histones, 97; Protamines, 97; Conjugated Proteins, 98; Glycoproteins, 98; Phosphoproteins, 98; Hemoglobins, 100; Detection of Hemoglobin, 102; Absorption Spectra of Oxyhemoglobin and Hemoglobin, 104; Derivatives of the Hemoglobins, 105 ; Fate of Blood Pigment in the Body, 107 ; Nacleoproteins, 107 ; Lecithoproteins, 109; Derived Proteins, 109; Primary Protein Derivatives, 109; Secondary Protein Derivatives, 111.

CHAPTER VI Some Fahiliak FooDBTDrps — Scue Ihportant Tisbues Some Important Foodstuffs, 114; Cooking and Preparation of Foods, 115; Milk, Il5; Butter, 116; Cheese, 117; Meats, 117; Eggs, 117; Vegetables, 117; BresdstufFs, 118; Choice of Diet, 118; Some Important Tissues, 119; Muscle, 119; Brain and Nerves, 120; Bones and Teeth, 121; Connective Tissue, 121; The Blood, 121; Reaction of the Blood, 123; Osmotic Pressure, 124; Ctnigulation of the Blood, 124; Lymph, 125; The Skin, 125.

CHAPTER Vn DioEBTioN IN THE Mouth General Purpose of Digestion, 126; Preparation of Food, 127; Saliva,

CHAPTEE Vril

Digestion in the Stouach

Importance, 131 ; Methods of Study, 131 ; Causation of Flow of Gastric Juice, 132; Qenerol Cbaiwiter of the Secretion, 134; Hydrochloric Acid, 134; Source of the Hydrochloric Acid, 136; The Functiona of the Hydroehlorie Acid, 136; Enzymes of the Gastric Juice, 137; Products of Peptic Digestion, 13S; Bennin, 138; Are Pepsin and B«nnin Identical^, 139; The Stomach Wall is Kot Digested, 140; Passage of the Food Into the Intes- Urn, 140.

CHAPTEE IX

Qeneral, 141; Pancreatic Juice, 141; Mechanism of Flow, 142; Compoeition of Pancreatic Juice, 142; Trypsin, 143; Eeunin, 144; Action on Fata, 144; Action on Starches, 144; The Bile, 145; Causes of Flow, 145; Composition, 146 ; Bile Pigments, 146 ; Bile Salts, 147 ; Intestinal Secretion, 147; Erepsin, 148; Other Eneymes, 148; Excretory Function of Intestinal BecTctiou, 148; Bacterial Action in the Intestine, 149; Feces, 160.

CHAPTEE X Absokftion General, 152; Absorption of Proteins, 153; Carbohydrate Absorption, 1S3; Absorption of Fats, 154.

CHAPTBB XI

General, 155; Physical Properties, 156; Volume, 156; Color, Transparency, 157; Consistency, Odor, Taste, 15S; Specific OraTity, 158; Total Solids, 1S8; Optical Activity, Beduciug Power, Fermentation, Etc., 159; Beaction, 160; Urea, 161; Uric Acid and Other Purine Derivatives, 163; Hippnric Acid, 166; Ammonia, 167; Creatinine and Creatine, 167; Inorganic Constituents, 160; Chlorides, 160; Phosphates, 170; Sulphates, 170; Carbonates, 171; Sodium, Potassium, Calcium, and Magnesium, 171; Pathologie&l Constituents of the Urine, 172.

CHAPTER XII

General, 173; Protein MetaboUam, 174; Amount of Protein Required, 176; Nitrogen Balance, 176; Carbohydrate Metabolism, 182; Sources of Glycogen, 187; Metabolism of Fats, 189; Metabolism of Inorganic Material, 190 ; Energy Exchange, 191 ; Utilization of Alcohol by the Body, 195 ; Starvation, 196; Unknown Food Constituents, 197; Vitamines, 197; Body Temperature, 199; Influence of Orgaus of Internal Secretion, 199,

TABORATORY WORK

Materials for laboratory work, 202.

CHAPTER I

General Laboratory Instkuctions General Laboratory Instructions, 208.

CHAPTER II

Dbtectios op the Elements and op Inorganic Salts

Carbon, SIO; Hydrogen, 210; Oxygen, 210; Nitrogen, 211; Sulphur, 211; Preparation of Muscle Extract, 211; Muscle Eesidue, 212; Blood Seriun, 212; Bone, 213; Tests for Inorganic Materials, 213; Chlorides, 213; Sulphates, 214; Phosphates, 214; Carbonates, 214; Calcium, 214; Magnesium, 214; Iron, 215; Sodium, 215; Potasaium, 216,

CHAPTER in

Cakbohtdbates

Monosaccharides, 217; Dextrose, 217; Levulosc, 221; Galactose, 221; Arabinose, 222; Diaaceharidea, 222; Saccharose (Sucrose), 222; Maltose, 223; Lactose, 224; Polysaccharides, 224; Starches, 224; Dextrines, 225; Glycogen, 226.

CHAPTER IV Fats and Phosphatids

Fats, 227; Phosphatids, Lecithin, 230.

Chapter V

Proteins General Protein Beactions, 232; Color Reactions, 232; Precipitation Tests, 234; Individual Groups— Simple Proteins, 237; Albumins, 237; Globulins, 23S; Prolamines, 240; Qlutelins, 240; Albuminoids, 210; Histones, 241; Protamines, 242; Conjugated Proteins, 242; Glycoproteins, 242; Hemoglobins, 243; PhosphoproteinB, 250; Nueleoproteina, 251; Lecithoproteins, 253; Derived Proteins, 253; Primary Protein Derivatives, Proteans, 253; Metaproteins, 253; Secondary Protein DeriTatives, 255; Proteoses, 255; Peptones, 256; Peptids, 257; Amino Acids, 257,

CHAPTEE VII Salivary Digestion Composition, 260; Digestive Action, 201.

CHAPTER VIII Gastric Digestion Preparation of ArtlHcial Gastric Juice, 264 ; Composition of Gastric Juice, 364; Digestive Action of Gastric Juice, 266; Motor Power of tlie Stomach, 26S; Bate of Absorption From the Stomach, 268.

CHAPTER IX

Pancreatic Digestion — Bile Pancreatic Juice, 260 ; Composition of Pancreatic Juice, 269 ; Digestive Action, 369; Intestinal Juice, 270; Bile, 270; Composition, 270; Effect of Bile on Surface Tension, 371; Biliary Calculi, or Gall Stones, 271.

CHAPTER XI

Qualitative Study Urinb Inorganic Constituents, 273; Organic Constituents, 275; Collection aiid Preservation of a Specimen for Quantitative Analysis — General Properties, £78; Quantitative Analysis, 281; Total Solids, 281; Acidity, 281; Total Nitrogen (Kjeldahl Method), 287; Ammonia, 290; Urea, 292; Uric Acid, 293; Hippuric Acid, 294; Purine Bases, 295; Creatinine (Folin), 295; Indican, 29G; AHantoin, 297; Oialie Acid, 297; Chlorides, 297; Sulphates, 298; Phosphates, 299; Pathologic Urine, 299; Proteins, 399; Carbohydrates, 303; Acetone Bodies, 306.

Appendix

Ammonium Thiocyanate, Standard, for Chlorides, 308; Barfoed's Solution, 308; Barium Chloride for Sulphate Detfirmination, 308; Benedict's Solution for Carbolij'drate Eatim&tion, 309; Congo Paper, 309; Esbach'i Beagent, 309; Fehling's Solution (Quantitative), 309; Fehling's Solution (Qualitative), 309; Folin-Schaffer Beagent, 309; Formalin (Neutral), 309; Gljioxflic Acid Solution, 310; Ouenzburg'a Beagent, 310; Magnesia Mixture, 310; Mett'B Tubca, 310; MIUod's Reagent, 310; Molisch'a Beagent, 311; Nylander's Beagent, 311; Pancreatic Solution {"Artificial Pancreatic Juice"), 311; Pepsin Solution (Artificial Gastric Juice), 311; Potassium Bichromate N/2, 311; Potassium Permanganate N/20, 311; Silver Nitrate (Standard) for Volhard Chloride Method, 311; Special Sodium Acetate Solution {for Uranium Acetate Method for Phosphates), 311; Stokes' Beagent, 311; Toepfer'a Beagent, 312; Uranium Acetate Solution (Standard), 312.

Chapter I Introductory

The Bcientific field known variously as Physiological, Biological or Biochemistry is the branch of science which treats of the chemical constitution, reactions and products of living material, whether of animal or plant origin. There ie a growing tendency to use the terms Biological and Biochemistry to donote the entire field, and to restrict the term Physiological chemistry to that portion of the subject dealing with animal material, but this practice is by no means general. It was once believed that the chemical processes going on in plants and animals were fundamentally different. Synthesis or building up was considered characteristic of plants, whereas animals were known to desynthesize or break down the substances which they ate. We now know that this difference is a quantitative and not a qualitative one, for if kept in the dark, plants take up oxygen, bum their constituents and give off carbon dioxide in a manner analogous to the process predominating in animals. Animals, on the other hand, are now known to be capable of performing numerous and elaborate syntheses, breaking down the materials of their food to simpler compounds, but rebuilding many of the fragments into tissue substance, or altering them to produce compounds having specialized biological functions.

IT

Object and Importance of Physiological Chena&try. — The ultimate object of workers in tlie field is to establish a rdationsbip between chemical composition and biological function, to be able to explain the workings of cells or of the various organs and tissues in terms of chemical reactions, but experimentors are still far from the attainment of this end, although many problems now are clearly understood which a few years ago were still unsolved. The findings of physiological chemists, and the methods of analysis developed by them have been of the greatest value to the science of medicine in general, and to the medical practitioner in particular. Since the body is made up of chemical compounds, and since many of its activities depend upon chemical reactions, it is obviouS' that any light thrown upon the nature and properties of its components will tend to make clearer the character of the reactions involved in the normal functioning of the tissues, thus furnishing a basis for the study and correction of abnormal or diseased conditions. Both diagnosis and treatment have come to depend more and more upon the findings of the physiological chemists, and the general advancement of medicine has been greatly furthered by the results of biochemical research.

Protoplasm. — Living material, whether of plant or animal origin has been found to consist of a substance which is strikingly uniform throughout the entire living world. This material has been given the name protoplasm (from the Greek words meaning "first," and "form"). It is a jelly-like watery mass, sometimes fairly rigid in form, possessing certain characteristics which serve to distinguish living from lifeless material. The first of these is the power of growth, — growth from internal forces such as we observe in animals and plants, and not growth from without such as the enlarging of a crystal. The second is Iho power of respiration, — taking up oxygen and giving off carbon dioxide. The third is the power of movement, — from place to place in animals, and movement incident to growth in plants. The fourth is irritability, and the fifth the power of reproduction. All living material possesses

INTRODUCTION 19

these five properties, and no lifeless material possesses all of tliero. Pbysiologicid chemistry may be looked upon as the stady of the chemistry of protoplasm, its products and the substance which it requires for the continuance of its normal ftmctions.

Matoial Bases. — Amounts in Body. — In beginning the study of so broad and complicated a field it is difficult to choose a point of attack. The most satisfactory plan will be first to become familiar with the chemical substances out of which living material is made up. The number of these compounds is naturally large, but for convenience they may be classified in five great groups which are given the name of the Base Materials, or Material Bases.

The five groups are as follows :

I. Inorganic materials including water.

n. Carbohydrates.

in. Fats, Phosphatids and related compounds. IV. Proteins.

v. Extractives.

Our first task will be to become familiar with the characteristics and properties of the Material Bases, studying group reactions and also the specific properties of important individual compounds, and methods for their detection and estimation. We will then trace the history of the various substances in their passage through the body, considering their fate in the alimentary canal, their subsequent behavior as constituents in the body tissues and fluids, and the final elimination of end products formed by their destruction.

The relative amounts of the different classes of Material Bases in the animal body are somewhat variable. Water and other inorganic materials make up about 65-70% of the entire body weight of which only 4.5-5% is ash and the remainder water. Carbohydrates are present only in small quantities, the amount being less than 1%. Fats and related compounds vary considerably in amount with the general state of the body,

20 PHTSIOliOGICAL eHEMISTBX

since they may be stored away in lai^ qaantities. The body contains on the average about 15%. Proteins vary less from an absolate standpoint, but relatively the percentage depends apon the amount of fat. The amount in the body averages also about 15%. Extractives, a heterogeneous group of compounds classed together because they are water soluble, and belong in none of the other classes, make Qp less than 1% of the body weight. This group will receive no further treatment as such, but the substances included in it (urea, creatinine, etc.) will be discussed individually in connection with the tissues or fluids in which they occur.

Chapter II Elements, Inorganic Materials, Water

Elementi Eotmd in the Bo^.—The body is made up of a large unmber of chemical elements which are present in very unequal amounts, and distributed quite unevenly in the various tissues and body fluids. Certain of these elements are in all living cells, others only in particular kinds of cells or in particular animals. Still others are present only accidentally or temporarily. The elements found most frequently are the non-metals carbon, hydrogen, oxygen, nitrogen, sulphur, and phosphorus ; the metals sodium, potassium, calcium, magnesium and iron; the halogens, chlorine, iodine, and fluorine. In addition, there are many other elements such as silicon, copper, manganese, arsenic, silver, lead, bromine, lithium, etc., found only in traces or only in a few animals,

Imporbmce Not Determined by Amount Present. — Three of the elements, carbon, hydrogen and oxygen alone make up over 90% of the body weight. The conclusion should not be drawn, however, that these are the only important elements and that those elements or compounds present in small amounts or traces are relatively unimportant to the organism. Quite the contrary may be the case. The body of an average-sized adult man contains only about three grams of iron, and yet this is so . necessary to life that an animal fed for some time on a diet which contains no iron will die quite as surely, though of course not as quickly, as if it had been deprived of food altogether. The principle involved may be formulated as the Law of the Minimum which states that the importance of a given substanee to the animal organism is independent of the relative amount in which it is required. Striking examples of this principle have developed in recent years, and we now know

22 PHYSIOLOaiCAI. CHBMISTBY

that the body requires certain compounds of which nothing was known a few years ago. Some of these substances appear to be organic compounds. Although the amounts of these materials of unknown constitution which are required by the body are only a small fraction of a gram, still their absence from the diet will cause severe disorders and ultimate death.

The importance to the body of the individual elements extends much beyond the function of serving as. inert building stones out of which the body materials are made up. Many of the chemical reactions in the body are greatly influenced or modified by certain of the elements. For example, two important processes, the clotting of the blood which tends to protect a wounded animal from bleeding to death, and the clotting of milk in the stomach, the first step in its digestion, are dependent upon the presence, among other things, of calcium, and without this metal neither of these reactions can occur.

The accompanying table gives a survey in round numbers of the relative amounts of the elements present in the body.

Carbon 17.5

Hydrogen 10.2

Oxygen 66

Nitrogen 2.4

Sulphur : 0.2

Phosphorus 0.9

Sodium 0.3

Potassinm 0.4

Calcium 1.6

Magnesium 0.05

Chlorine 0.3

Iodine Traces

Fluorine Traces

Other elements Traces

Carbon, HydToe:fln, Oxygen, mtrosen, Snlphtir and Phosphorus. — Carbon has the property of forming a very large num-

D,„l,zccDyG00gle

ELEMENTS, INORQANIC MATERIALS, WATER 23

ber of compounds with hydrogen, oxygen, and Bometimes sulphur, phosphorus and other elements. These compounds are so numerous that a separate branch of chemistry is devoted to them under the name of organic chemistry. Thirty per cent or more of the body consiBta of organic material, or compounds of earbon with hydrogen, oxygen, etc. The importance of these compounds is so great that special chapters will be devoted to the important groups. The body reeeives its carbon compounds in the foods, the solid portion of which is very largely organic material. Aside from the organic components of the tissues, earbon is also found in inorganic form, chiefly as calcium carbonate in bone, and as sodium bicarbonate in the blood. This latter compound is of great importance, since, although its solution is neutral, it has the power of neutralizing acids, thus protecting the tissues when acids are introduced into the blood either from the digestive tract or as the result of the breaking down of body materials. Carbon is eliminated from the body as carbon dioxide, given off through the lungs, or as more complex compounds snch as urea and other materials excreted in the urine or the feces. If heated, organic compounds char, leaving a black residue of carbon.

Hydrogen and oxygen aside from being constituents of water, organic and inorganic compounds, also play more specialized roles in the body. Oxygen, which makes up about two-thirds of the entire body weight is taken up as a constituent of the compounds in the food and in the process of respiration. Hydrogen, the presence of which in ionic form is the distinguishing characteristic of acids, plays an important part in the digestion of proteins by gastric juice. Hydrogen and oxygen are eliminated from the body chiefly as water and CO, given off through the lungs, and as water and in organic compounds in the urine and feces. On heating organic materials they decompose, and the hydrogen and oxygen are given off as water and various other eompounds.

Nitrogen, sulphur and phosphorus also play various roles in the body and all three are found both in organic and inorganic

24 PHYSIOLOdlCAL CHEMISTRY

compounds. Nitrogen is a constituent of all proteins. Many proteins contain sulphur and phospbonis as well. Nitrogen occurs in various other compounds throughout the body, and the body fluids contain gaseous nitrogen in solution, as is to be expected since nitrogen is somewhat soluble in an aqueous liquid, and in the lungs the blood comes in contact with the air which is made up about four-fifths of nitrogen. So far as ia known this dissolved nitrogen has no influence on the body's activities. Nitrogen is excreted mainly as urea, uric acid and other products formed by the decomposition of proteins in the body. If heat«d with soda lime, an organic substance of this type gives off its nitrogen as ammonia. Sulphur and phosphorus are present in various compounds other than the proteins. Of these the phosphatids are perhaps moat interesting. This group will be considered later. Calcium phosphate makes up about 85% of the ash of bone. Sodium phosphate is found in the blood and tissues. Sulphur and phosphorus are excreted mainly in the urine as sulphates and phosphates, but also in the feces. Unoxidized sulphur may be split off from organic compounds by boiling with alkali. On adding lead acetate, a dark precipitate of lead sulphide will form. This teat may be confirmed by adding an acid. Hydrogen sulphide will be given off and may be identified by a paper moistened with lead acetate on which lead sulphide will form as a shiny dark precipitate. Sulphates are detected by precipitating as barium sulphate. Phosphates are detected by precipitating as ammonium phosphomolybdate.

Sodium, PotaBsinin, Calcitiin, Magnesiiim and Iron. — These metals make up only a small part of the body, but they are none the less important. They are distributed widely throughout the body tissues and fluids. There usually is more sodium than potassium in body fluids, and more potassium than sodium in the solid tissues. These metals are present as chlorides, sulphates or phosphates. Sodium chloride in the blood is interesting since it furnishes chlorine for the hydrochloric acid of the gastric juice, whereas sodium bicarbonate is very important in

EXBMBNTS, INORGANIC MATERIALS, WATER 25

preserving the neutrality of the blood aa above noted. Sodium chloride is the only inorganic substance which ia contained in a mixed diet in amounts insufficient for the body's needs. Accordingly our food must be salted. Herbivorous animals, living on plants in which potassium is in excess of sodium, crave salt, and it is well known that cattle must be "salted" to keep them in good health. Sodium and potassium also affect the irritability of muscle and nerve tissue so that their role in the organism may perhaps include little understood regulatory functions. These metals may be detected by the flame test or by precipitation as sodiuni pyroantimonate or potassium cobaltinitrite.

Calcium and magnesium, while found in all cells in the body, are present in largest amount in the bones and teeth, which contain about 99% of all the calcium and 70% of all the magnesium in the body. Their phosphates and carbonates make up about 98.5% of all the inorganic material in bone. That these metals have other roles to play in the body, however, is demonstrated by the failure of blood and milk to elot in the absence of calcium. Calcium is detected by precipitation as calcium oxalate. Magnesium is present in much smaller amounts than calcium, and less is known of its physiological activities. It is interesting in this connection that magnesium sulphate acts as an anesthetic on mammals and that it paralyzes the endings of the motor nerves in the muscles. Magnesium is detected by precitation as magnesium ammonium phosphate.

Iron, though present only to the amount of a few grams In the body of an adult man, still is distributed very widely. Its most conspicuous role is in connection with the hemoglobin of the blood, of which it is a constituent. This substance carries oxygen from the lunge to the tissues. Iron probably is present also in traces of inorganic iron compounds. The spleen contains relatively much, so that it has been suggested that the spleen has some role to play in connection with the iron compounds of the blood. Also the liver is concerned with the fate of hemoglobin, and serves as a clearing house through which hemoglobin from worn out corpuscles is broken down and excreted by way of the bile into the intestine. Iron is also excreted in the urine, the amount being no greater than 10 or 11 mg. per liter.

Iron ia detected by precipitation as "Prassian Blue" or ferric ferrocyanidc or by the formation of ferric thioeyanate which is red in color.

Oblorine Iodine, Fluorine etc. — Chlorides are present in traces in all the tissues and fluids ; the blood contains about 0.4% sodium chloride, the gastric juice about 0.4% hydrochloric acid. The necessity of adding sodium chloride to the diet has already been referred to. Chlorides are excreted iu the urine in amounts varying with the amount in the food, 10-12 gms. daily being an average figure. Chlorine may be detected by precipitation as silver chloride. Iodine ia interesting chiefly in connection with its occurrence in the thyroid gland. This gland, by means of a compound which it produces and pours out into the blood stream, has far reaching influence on the chemical reactions going on in the body. This important aubatance is an iodine compound. If an iodide gets into the blood stream, the salivary glands have the power of excreting it. After taking a capsule containing potassium iodide, iodine may be demonstrated in the saliva. Fluorine is found in the bones and teeth.

Other elements may occur either regularly or accidentally in the body tiaaues or fluida, but usually only in traces.

Water. — Water makes up about % of the body weight of mammals, and a much larger part in some lower animals. All tiasues contain it, even the enamel of the teeth: blood, lymph, the digestive juices, urine, etc., are ?4o-%o water; the organs and softer tissues about %. Water serves a variety of functions. It is the circulating medium for transporting food and waste material to and from the cells, it holds various substances in solntion and makes ionization possible, and is a medinm for the excretion of waste. It also distributes the heat of the body, and by evaporation from the akin is instrumental in regulating body temperature. An animal may survive for many days without nourishment, but if water also is withheld, death follows in a few days' time.

,Go

Chapter III Carbohydrates

Ctnnposition, Occurrence, General Fimotion. — The earbohy* drates are compounds of carbon, hydrogen and oxygen in which the hydrogen and oxygen are present usually in the same proportions as in water, hence the name of the group. A few carbohydrates do not conform to this general statement, for example Rhamnose CjHijOb. Some substances not carbohydrates do contain hydrogen and oxygen in this proportion, such as acetic acid CjH.Oj and lactic acid CaHaOj. Thus, this characteristic is not distinctive of the group. Carbohydrates vary considerably in their properties. They are found both in plants and in animals, but chiefly in the former, in which they form a considerable part of the structural frame work. In animals they serve mainly as a fuel to be oxidized for the production of heat or the performance of mechanical work, but they may be laid away as a reserve store to be called on in case of need.

Stractnre of the Carbohydrates. — The carbon atoms in the carbohydrate molecule are linked together in a long chain. It has been shown that the molecule contains several hydroxy] groups, and that in the simpler members of the group at least

H

I I

there is either an aldehyde — C ^ or a ketone C = group.

I I

The remaining valencies of the carbon atoms in the chain hold the hydrogen atoms not accounted for. Thus the formula for glucose, one of the most important carbohydrates, has been shown to be as follows:

PHXSlOLoaiCAL CHEUISTBT i-o

H— 0— OH

I

HO— 0— H

I

H— C— OH

I H— C— OH I OH.OH

An example of a sugar containing a ketone group is fructose, which has the following formula:

I HO— C— H

I H— C— OH

I H— C— OH

Fructose

Many of the reactions characteristic of the carbohydrates depend upon the properties of the aldehyde or ketone groups which they contain. In the case of the more complex carbohydrates, these reactive groupings are usually combined in such a way that they do not show their characteristic behavior.

Optical Activity On inspecting the above formuln for

glucose and fructose it will be observed that the hydrogen and hydroxyl groups of the four carbon atoms occupying the middle portion of the chain are not arranged in a regular manner.

CABBOHYDBATES 29

This irregular arrangement is intended to indicate that there is aetiially a variation in the arrangement of these groups around, the carbon atoms in space. This arrangement is a determining factor in the property of these substances known as optical activity. Optical activity is the property possessed by many compounds of rotating the plane of polarized light.

If a ray of white light is passed through a crystal of Iceland spar it is split into two slightly diverging rays, but this is not the only change which is produced in the ray. Light is due to vibration of the particles of the ether, the vibration being at right angles to the direction of the ray, and in all possible planes passing through the path of the ray as an axis. We can picture this perhaps by imagining the cross-section of a ray of light to resemble the crossssection of an orange, only with many more planes of vibration. After passing through the crystal of Iceland spar, the light is so altwed that in each of the two emerging rays vibration is taking place in only one direction. To light of this character is given the name plane polarized light. It has been found that optically active substances have the property, if such a ray of light is passed through their solutions, of rotating the plane in which the ether particles are vibrating, some substances rotating the plane of vibration to the right, others to the left. Not only do these compounds possess this property, but a g^ven substance, under similar conditions of observation (concentration, temperature, etc.) always rotates the plane of polarized light through the same angle. This uniformity of behavior on the part of each optically active substance gives us a most useful means of detecting the presence of the compound in question.