THE .PHYSIOLOGY OF FOOD AND ECONOMY IN DIET/ BY W. M. BAYLISS, M.A., D.Sc. (OxoN.), F.R.S., ETC. PROFESSOR OF GENERAL PHYSIOLOGY IN UNIVERSITY COLLEGE, LONDON LONGMANS, GREEN AND CO. 39 PATERNOSTER ROW, LONDON FOURTH AVKNUK & SOrn STREET, NEW YORK BOMBAY, CALCUTTA, AND MADRAS 1917 PREFATORY NOTE THIS little manual has arisen from a course of public lectures given at University College, London, in October and November, 1916. It has been thought that a useful purpose might be served at the present time by making these lectures more generally accessible. Although no previous know- ledge of physiology is assumed, references are inserted to sources of more detailed information on certain questions for those readers who may desire to enter more deeply into these questions. Occasionally, points of interest are indicated which, though un- essential to the main argument, will be found to appeal to the reader possessing the necessary scientific preparation. I would especially acknowledge my in- debtedness to the booklet by Wood and Hopkins, Food Economy in War-Time. 364736 vi PREFATORY NOTE It may be pointed out that the problems involved are not only of importance in war- time, but also in times of peace, since waste should always be avoided, as far as possible. W. M. B. CONTENTS CHAP. PAGE I THE PROBLEM AS A WHOLE i II THE USES OF FOOD 6 1. Growth 2. Maintenance 3. Work Energy Constituents of the Body and of Diet Proteins Oxygen III THE THREE CLASSES OF FOOD STUFFS . 25 Proteins Fats Carbohydrates IV THE QUANTITY REQUIRED ... 32 "Man Value" Food Available Belgian Food Commission Actual Values of Food Stuffs Protein Minimum Use of Carbohydrate Use of Fat V ACCESSORY FACTORS, OR "VITAMINES" . 56 VI DIGESTIBILITY 61 vii viii CONTENTS CHAP. PACK VII ALCOHOL . . 67 VIII VEGETARIANISM 75 IX EXERCISE 77 X THE VALUE OF COOKING . . .80 XI CHARACTERISTICS OF CERTAIN ARTICLES OF DIET 82 Bread Other Articles XII POSSIBILITIES OF ECONOMY ... 90 XIII GENERAL CONCLUSIONS .... 97 REFERENCES 101 INDEX ...... 105 THE PHYSIOLOGY OF FOOD AND ECONOMY IN DIET CHAPTER I THE PROBLEM AS A WHOLE ALTHOUGH many physiological problems have been brought into prominence by the War, mostof these concern people as a whole only indirectly. That of Food, however, is of immediate interest to us all. Leaving on one side that aspect of the matter which may be regarded as, in a sense, aesthetic, associated with the gratification of the sense of taste, it may be taken for granted that every one is sincerely desirous of avoiding unnecessary consumption of food, so far as it can be done wisely and without diminution of value of the individual as a member of the community. We have to inquire, therefore, into the uses of food, into the amount necessary to fulfil 6 2 PHYSIOLOGY OF FOOD these uses, into the necessary constituents of an adequate diet, and into the ways in which these constituents can be supplied most econo- mically. Some subsidiary questions will need brief discussion, such as the part played by digestion and the use of alcohol. It is, indeed, remarkable how widespread is the impression that butchers' meat has some specially valuable properties ; and that sugar, amongst other things, should not be regarded as a food in the true sense of the word. Again, there are some people who appear to be under the belief that the more food eaten the better, so long as it is digested, We hear of a "fine healthy appetite," when the person spoken of is probably really consuming much more than he needs. We shall see later that there is no probability of any actual deficiency in the food supply as a whole, although there is undoubtedly already some scarcity in particular articles of diet, and prices have risen all round. We want to know how far we can avoid costly articles or replace them by cheaper ones, without any disadvan- tage. It is scarcely necessary to remark THE PROBLEM AS A WHOLE 3 that saving in unnecessary expense enables more money to be devoted to national needs, as by purchase of War Loan and so on. Here we may note that the problem is not merely a physiological one, it is a complex one of economics also. I call attention to this point, although it is outside the scope of the present inquiry. If, for example, a great demand were to arise for some particular article of food on account of its cheapness, this demand in itself would produce a rise in price. It seems that the best course to take to avoid economical disturbance is that indicated by Wood and Hopkins (1916, p. 3 ; see List of Literature at the end of this book). This is, that articles whose price is either falling, or only slowly rising, should be selected rather than those whose price is rising quickly. This of course implies an observation of the market prices from day to day. We may hope for guidance in this respect from the Government Departments. It may be well, before we proceed further, to state the general conclusion to which we shall arrive. This is, that any kind of diet 4 PHYSIOLOGY OF FOOD which is at all likely to be chosen in the British Isles will contain all that is necessary, provided that it be taken in the right amount. Even potatoes alone, under favourable conditions, can be made to suffice, as we shall see later. It is not in the least probable that any reason- able person here would attempt to live only on polished rice, still less on a pure chemical product such as cane-sugar or olive oil. In the succeeding pages, I attempt to give, in as simple and elementary a manner as possible, the essential facts of the science of nutrition. At the same time, I do not feel compelled to avoid occasional reference to somewhat more difficult aspects of the sub- ject, but only where they may be of interest to readers already in possession of some physiological knowledge and where they may be omitted by others without loss of what is of immediate practical importance. It may happen, of course, that readers of the latter kind will be deprived of the proof of some statements which rest on the more difficult parts of physiological investigation. I must ask them to take such statements on trust. THE PROBLEM AS A WHOLE 5 We will proceed to discuss, in order, the reasons why food must be taken, the essen- tial components of food, the quantity of these required, and finally some practical sugges- tions following from the physiological facts brought forward. CHAPTER II THE USES OF FOOD 1. Growth. When a living being is in- creasing in size, it is perfectly obvious that materials must be supplied for the purpose, and that the supply must contain in some form the actual chemical constituents of the new tissues formed. 2. Maintenance. Even in the adult, the various parts of the body undergo waste by wear and tear, just as any other machine does. This loss must be replaced, and again material containing the chemical elements of the substance lost must be supplied. When we say this, it is not to be understood that the same actual chemical compounds as those contained in the body must be given in the food. But, since chemical elements, except under very special conditions, cannot be THE USES OF FOOD 7 changed into other elements, food which con- tains some compounds of the elements found in the body must be taken. For example, new growth contains compounds of nitrogen ; therefore, food containing nitrogen must be available. These two functions of food are very closely related, although not necessarily iden- tical. Under certain circumstances, more- over, as in the training of an athlete, new muscular substance is produced. So that, even in the adult, material for actual growth is sometimes required. 3. Work. But the greater part of the food, both in the young and in the adult, is needed for a different purpose, a fact which is frequently apt to be overlooked by those who are unfamiliar with scientific studies. While the addition of new substance and the replacement of that lost are sufficiently plain to most people as requiring food, the necessary consumption for the purpose to which I am now referring is somewhat intangible. One of the most characteristic of the 8 PHYSIOLOGY OF FOOD properties of living beings is the perpetual change shown by them : they are always doing something, as one may say. Now, universal experience teaches us that such activity means doing work, and that this im- plies the loss of something by the worker. The capacity of doing work is called energy, by physical science. An extremely impor- tant fact, on which the whole of science is based, is that energy can be measured exactly. And the loss of energy in doing work is pre- cisely equivalent to the work done. Having measured by an appropriate method a par- ticular amount of energy, we know that we can obtain from it just so much work and no more. As a matter of course, then, if work is to be done by our muscles, they must be supplied with a source of energy. This is done by what we may call, with justification, combustible substances in food. The fact that work can be obtained from the burning of coal under a steam-boiler is familiar to every one. There are numbers of similar materials which burn in air, and one of the most instructive experiments which can be THE USES OF FOOD 9 performed is the very simple one of showing that the products of the combustion of sugar in air and those found in the air which we expel from the lungs are identical. These latter arise from the burning of sugar and other foods in our bodies for the purpose of affording energy to perform work. An im- portant practical fact which follows naturally from what has just been said is, that the greater the quantity of work done the more fuel is required. Probably one of the most significant results of modern physiological research, is that there is an exact balance between the energy taken in and that given out in the form of work of various forms. From this, again, it is plain that energy may exist in different forms ; the chemical energy of the food is transformed partly into that of muscular contraction, partly into heat, and so on. But none is lost and none is ever created. Some readers will doubtless recog- nize this statement as what is known as the first law of energetics, that of the conservation of energy, and it is one of the greatest modern physiological achievements to have shown 10 PHYSIOLOGY OF FOOD that it applies no less to man than to inani- mate nature. We see that food is required for two main purposes : (i) for growth or repair of bodily substance ; (2) to afford energy. Since a great variety of different materials are capable of being burnt up for this latter purpose, although they may not contain what is wanted for growth, it follows that the requirements are different for the two purposes. While the food stuffs needed for growth and main- tenance do, as a matter of fact, contain combustibile constituents, and thus give energy, there are other food stuffs, which are equally valuable as producers of energy, but insufficient for growth. The general facts may be better under- stood by comparison with a petrol motor. Such a machine in process of construction requires certain materials steel, iron, brass, insulating material and so on some of which cannot be replaced by others. When finished, and set to work, a supply of these materials is no longer necessary, but a combustible fuel is used as food for the engine. This fuel is THE USES OF FOOD 11 burned in the cylinder, and the energy afforded can be made use of for various purposes. Notice that the fuel does not become part of the motor, but that its energy is made available by means of the mechanism. Now, in process of time, certain parts, such as the piston rings and valves, wear out and must be replaced by new ones, whereas there are other parts, such as the fly-wheel and the general framework, which last for the dura- tion of the life of the engine, except for accidents. There are also other suggestive points of resemblance to the animal machine. Attention will be directed to these later. Proceeding now to further details, we may first consider the nature of the food necessary for growth and maintenance. Examining the constituents of the animal body, we find that they consist of numerous compounds of carbon with nitrogen, hydro- gen and oxygen. Some of these contain also sulphur and phosphorus. In addition to these, there is a large amount of water and a small amount of some inorganic salts, chiefly of sodium, potassium and calcium. 12 PHYSIOLOGY OF FOOD As regards water, this does not afford energy, since it is already completely burnt or oxidized. But it may be looked upon as a kind of food, in so far as it is necessary for the proper working of the animal machine, and may be compared to the lubricating oil used for the moving parts of the petrol motor. As water is continually being lost from the lungs and kidneys, it must be re- placed. In civilized and habitable places there is, or ought to be, a copious supply of good water, a matter which is by no means the least important one to ensure. As regards salts, similar remarks may be made. The machine will not work without them ; but, except under special conditions, they are taken with other forms of food, being contained therein. The only salt com- monly consumed as such is sodium chloride, ordinary table salt. Further remarks in connection with water or salts will not be required. What about the carbon compounds which form the greater part of our bodies ? As is well known, the large body of doctrine THE USES OF FOOD 13 known as organic chemistry is concerned with these, and the name is due to the fact that the first compounds of this kind were obtained from plants or animals. We may ask why the compounds of carbon should have this special place of honour. It is interesting to consider for a moment what are the peculiarities of carbon that have caused it to be the basis of the evolution of life. In the first place, carbon is quadri- valent, as the chemists call it ; that is, it can combine with four other elements or groups. Moreover, its atoms possess in a special degree, unknown in the case of other ele- ments, the power of combining with each other, so that long chains or rings are formed. Compounds containing as many as two hun- dred or more atoms are known to exist. Another important fact about carbon is its position with respect to other elements with which it may combine. The chemical ele- ments can be arranged in a series, such that those at opposite ends have the greatest 4 ' affinity " for each other. In other words, .they combine together with the setting free 14 PHYSIOLOGY OF FOOD of large amounts of energy. Oxygen and hydrogen, for example, are a long way apart in this arrangement, and they combine with great violence. Now, carbon is somewhere about the middle, so that it can combine with either hydrogen or with oxygen. In the latter case, we have the universal product of combustion of carbon compounds as it takes place in living organisms, as well as in the non-living world. This is carbon dioxide or carbonic acid, as it used to be called, since it forms an acid when dissolved in water. In this process of combustion, energy is given off. On the other hand, carbon can be made to combine with hydrogen, giving rise to the well-known paraffin oils and similar hydro- carbons. But, in this case, energy must be supplied from outside. These compounds of carbon and hydrogen, when burnt, give out large quantities of energy, as is familiar to all, at all events in one of its forms, that of heat. We see thus that carbon serves as an admirable means for the transference of energy in vital processes. The carbon compounds in the form in THE USES OF FOOD 15 which they leave the animal body, after being made use of, are, nearly all of them, completely burnt up, so that they contain no more available energy, or merely a negli- gible quantity. It is clear, therefore, that some means must exist for converting them back again into food-stuffs containing energy. A description of this means is beyond the scope of this book ; in brief, it may be stated that it is provided by the green plant, with the aid of energy derived from the rays of the sun. This energy is stored up in the form of compounds from which the oxygen has been partially removed, which then serve as sources of food to give energy to the animal. Thus, our energy is derived from the sun. Further details may be found in my General Physiology (1915), pp. 558- 569- Animals are dependent for their food either on plants or on other animals, that is, ultimately on plants in all cases. Since all the constituent parts of the body structures contain nitrogen, food must be supplied containing this element. The 16 PHYSIOLOGY OF FOOD simplest chemical compounds of this kind which can be used by the higher animals are those known as amino-acids. One of these is formed from acetic acid, familiar in vinegar, by the combination with it of a derivative of ammonia, which contains nitro- gen. There are a large number of different amino-acids, and together these have been found capable of serving as nitrogen food, without the addition of other nitrogen com- pounds. But, as a regular diet, they would be impossible on account of the difficulty and cost of preparing them, apart from ob- jection on the ground of taste. Accordingly, what we actually use are the various com- pounds, consisting of amino-acids united together, which are found in the tissues of plants and animals. These compounds are known as "proteins," a name which will be frequently used in succeeding pages, and has even become familiar from the pages of the daily press. Certain of these proteins con- tain sulphur and phosphorus, so that the supply of these elements is provided for. The word " proteid " is now obsolete. THE USES OF FOOD 17 In actual practice, very few foodstuffs are of such a nature that they can be used by the cells of the body without being split up into simpler substances. Proteins, for ex- ample, must be converted into amino-acids, and starch into sugar. This is the function of the process known as digestion, to which our attention will be devoted presently. An important point with regard to the materials required for growth is that different proteins are composed of different mixtures of amino-acids, such that one or more may be absent from a particular protein. Such a protein, therefore, would only be an adequate source of nitrogen if the amino-acid wanting could be formed in the body from those which are actually present in the food itself. But there are some amino-acids which cannot be so formed. A protein which does not contain them is accordingly not, of itself alone, adequate as a source of nitrogen food. Such a contingency is not likely to happen in the British Isles, but must not be for- gotten where there is a possibility of a limited variety in protein diet. 18 PHYSIOLOGY OF FOOD It may be remembered that, in our illustra- tion of the petrol motor, it was pointed out that there are parts which do not require renewal on account of wear and tear. It is not unexpected to find that, after the work- ing machinery of the body has been con- structed, certain parts of it also do not appear to suffer loss in this way. Hence, a particular constituent of food may be necessary for growth, but not for main- tenance. Some experiments made in the United States seem to show that this is actually the case. The important fact, however, for our pre- sent purpose, is that the products of wear and tear contain nitrogen, both in the adult and in the growing child. Turning next to the second function of food, the supply of energy, there are a few more facts needed in order to make further discussion intelligible. While there are many forms of energy mechanical motion, heat, electricity and so on these can be converted into one another. Indeed, practically all the energy which we THE USES OF FOOD 19 make use of is derived from the chemical energy of the food taken. This food, when burnt by the oxygen taken in by respiration, sets free energy which is converted into the various forms required. As Clark Maxwell has put it, the transactions of the material universe are carried on by a system of debit and credit in which energy changes hands, as it were. Now, it is just in this transfer of energy that the phenomena which par- ticularly strike us as characteristic of living beings are manifested. It is while in the act of transference that it is especially capable of being made use of. Just as in com- mercial transactions money can be most readily appropriated when passing from one form to another. From another point of view, while life lasts there cannot be a real state of equilibrium. Life means activity, and activity means transfer of energy. When it was stated above that all forms of energy can be changed into one another, it must not be understood that the whole of any one form can be changed into the equivalent value in any other form. While 20 PHYSIOLOGY OF FOOD this is true for all forms of energy with the exception of heat, in this latter case the whole cannot be converted into another form of energy. This fact impresses upon us the consequence that, when once energy has become heat, a part of it is lost for other useful purposes. It is no longer "free" energy, and is sometimes said to be exclusive use of polished rice. ACCESSORY FACTORS 59 Further, there is evidence that they may be divided into two groups, neither of which is effective for growth without the other. McCollum and Davis (1915) find that rats will not grow on polished rice, even if wheat germ be added ; nor will they grow if butter alone is added. Both together made the diet an adequate one. That contained in wheat germ is soluble in water, not in fat, and may be called the " water-soluble B factor," the other is the " fat-soluble A factor." From Hopkins's experiments, fresh milk must contain both of these. It has been noticed in experiments on the effect of absence of these factors, that the deleterious effects do not come on at once. They are subject to a delay of some days. This shows that they do not rapidly dis- appear, although they must be present in very small quantity. The fact indicates that they do not undergo chemical change, like the foodstuffs properly so called. The way in which they act is unknown, but the chemist will be reminded of the phenomena called "catalytic." The mode of action of 60 PHYSIOLOGY OF FOOD the digestive agents known as " enzymes" is also catalytic. An interesting fact is that plants are dependent for normal growth on similar factors. The first case in which the ques- tion was investigated was that of yeast, by Wildiers in 1901. This work was done at the ill-fated University of Louvain, whose wanton destruction has aroused the execra- tion of all civilized nations. The more recent work of Bottomley indicates that these plant factors may be destined to play an important part in the cultivation of vegetable foodstuffs. The practical application of the facts described in this section is that in a diet composed of a fair variety of foodstuffs, inclusive of fresh vegetables or fruit, there is no risk of absence of the necessary acces- sory factors. But when a monotonous diet is taken, such as rice, it is important that the material should not be too much pre- pared by artificial means, such as the polish- ing of rice to produce a white appearance. CHAPTER VI DIGESTIBILITY THERE are many constituents of foodstuffs as bought which are not digested at all, although, if burnt in air, they are capable of giving energy. This has already been men- tioned incidentally. Materials of this kind are the cellulose constituents, woody fibres and so on of plants and some parts of the fibrous or tendinous parts of meat. These, of course, must not be reckoned as com- ponents of the daily ration. They have their value, however, in promoting intestinal movements. There are also some constituents which are only partially utilized, because they are not quickly digested and do not remain long enough in the alimentary canal to be fully acted upon. Such are the proteins of nuts. 61 62 PHYSIOLOGY OF FOOD In giving to such proteins their proper value, therefore, it must not be reckoned as that of the total content in protein, but only some 8o%of it. Tables in which the proportion digested of various foods is shown will be found in Lusk's book (1909). Many facts of practical importance have come to light through Pavlov's experiments (1910), especially as regards gastric diges- tion. In the first place, it was found that the mere presence of food in the stomach was insufficient to excite secretion of gastric juice, except after some considerable time. The chief stimulus is that the food should be approached with appetite, the stimulus being conveyed through the nervous system. With- out appetite, scarcely any gastric juice is formed. When Macbeth wishes for his guests that good digestion may wait on appetite, it seems that he was stating a truism. The value of attractiveness in food preparations is shown hereby, as is also the mistake made by some well-meaning food reformers who would wish to confine us to plain food. Of course, mere ornamentation of cakes and con- DIGESTIBILITY 63 fectionery is wasteful of time and material, but variety in form and flavouring, as also in mode of preparation, is to be approved of. This would especially apply to the present time, when it is desirable to limit the consumption of meat. It is important to distinguish between hunger and appetite. The former, as shown especially by Carlson (1916), rests upon sen- sations derived from muscular contractions of the empty stomach. The latter is rather an anticipation of pleasures to be obtained from sensations of taste. Hunger, as Carlson re- marks, is probably never felt by many people at the present day, because the physiological state is absent. The gastric contractions in question originate in the stomach itself and are of quite a different nature from those which take place during the process of di- gestion. These latter serve to bring in turn all the food under the action of the digestive juices, and, in due course, propel it into the next following section of the alimentary canal. It was mentioned above that, although the presence of food in the stomach by itself 64 PHYSIOLOGY OF FOOD alone does hot lead to any immediate secre- tion of gastric juice, after a time some secretion appears. This is due to the direct effect of products of digestion and is produced also by introduction of meat extracts and other substances into the stomach. The use of soup to commence dinner with finds its justification in this fact, especially when fatigue has blunted the appetite. Perhaps bitters or vermouth may sometimes be use- ful under such conditions, but alcohol in any form must be regarded as an aid of psychical import only. Its direct effect on all digestive processes is a retarding one. Carlson (1916, pp. 293 and 297) shows that bitters, used medicinally, neither increase hunger nor pro- duce any effect on the amount or activity of the gastric juice. There are one or two erroneous impres- sions as to the value of some particular foods that need correction. The first of these is that raw eggs are more easily digested than cooked ones. The contrary has been shown by careful experi- ments to be the case. Of course, if the DIGESTIBILITY 65 white is boiled hard, it must be finely divided by chewing, otherwise the gastric juice can only attack it slowly from the outside. Prob- ably the best form is that of custard. The reason why raw egg-white is difficult of digestion is that it contains something, in small amount, which has a powerful retarding or inhibiting action on the digestive enzymes. This is destroyed by heat. Arrowroot and cornflour are popularly supposed to be specially digestible foods for invalids. In fact, they are chiefly starch, and apparently no better than other forms of starchy food. Very little protein is contained in them. Gelatin, again, is not a complete protein and should not be relied upon to any extent to replace true proteins. These considerations are of importance in feeding patients recovering from any wasting disease. It will be obvious that they require plenty of material to build up the tissues that have been lost. Fatty substances are not digested in the stomach and, as Pavlov showed, tend to oppose the secretion of gastric juice. In a 66 PHYSIOLOGY OF FOOD healthy stomach, and especially when in a finely divided state, as in milk and cream, they produce no disturbance and are easily digested in the small intestine. This applies, as is well known, even to the case of illness. CHAPTER VII ALCOHOL AT this point some further remarks with regard to the use of alcoholic "stimulants" are necessary. Some intemperate advocates of Temper- ance have unfortunately done harm to their cause by making statements which their opponents are able to disprove. One of these is the denial that alcohol is in any sense a food. Its energy value, when burnt outside the body, is high, amounting to 708 calories for 100 grams as against 400 for carbohydrate or protein. It has been stated that it is not burnt in the body, or only to a very slight extent. This is not true. It is excreted unaltered in small amount after considerable quantities have been taken, but by far the greater quantity is oxidized to afford energy. 67 68 PHYSIOLOGY OF FOOD The real objections to its use are of another kind and chiefly on account of its action on the brain before it has had time to be burned up. Although it appears to be a stimulant, this impression is due to an incorrect interpretation of the effects ob- served. It is really a narcotic. One of the most striking facts with regard to the activities of the highest parts of the brain is the great predominance of the inhibitory mechanises, by which the bringing into play of inappro- priate movements or sensations is kept in check. Now, these mechanisms themselves are extraordinarily susceptible of being abo- lished by extraneous influence of various kinds. One of the most powerful of these influences is alcohol. When, therefore, greater liveliness is experienced under its action, it is because alcohol paralyses the inhibiting mechanisms and not because it excites activity by a true stimulating action. There are, on the other hand, certain sub- stances which appear to be genuine stimulants. Such are caffeine, a constituent of coffee and t;ea, and perhaps some of the substances ALCOHOL CO found in meat extracts. Liebig's extract, for example, contains very little real food. Cocaine, in small doses, has also a stimulant effect on the brain, but it must on no account be used for this or any other purpose except for local anaesthesia, and indeed it is only required for this purpose in very rare cases, since other drugs, such as novocain, serve the purpose equally well. The cocaine habit is easily formed and soon makes a total wreck of its victim, body and mind. Some proprietary articles sold for asthma and other purposes sometimes contain cocaine and should be warned against, although the pre- sent restrictions make it difficult to obtain them. An experiment made by Pavlov in his in- vestigations of the activities of the brain shows how readily an act in which inhibition plays a part can be upset by a removal of the inhibition. It was this : a particular bell was rung in the hearing of a dog. Two minutes afterwards food was given. The giving of the food was accompanied, as usual, by the secretion of saliva. The process was re- 70 PHYSIOLOGY OF FOOD peated for a number of times and then the bell was rung without the subsequent present- ation of food. Nevertheless, after the due interval of two minutes, saliva appeared. It is clear that something must have been going on in the brain between the hearing of the bell and the secretion of saliva, but that the result was prevented by inhibition from show- ing itself. That this was the case was proved by the fact that the inhibition could be re- moved by the application of some indifferent stimulus, such as a touch, to the animal's body. Such a stimulus is not by itself associated with the secretion of saliva. But, if it be applied during the interval of two minutes spoken of, the saliva appears imme- diately, instead of waiting for the lapse of the proper time. The narcotic effect of alcohol on the brain is also shown in other ways. After even small quantities, the ability to add figures correctly is decreased, although the subject believes that he is doing it unusually well. Moreover, the effect lasts for as long as twelve hours or more. ALCOHOL 71 Another false idea is that alcohol warms. This is due to the fact that it dilates the blood vessels of the skin ; and, since the feel- ing of warmth arises from the skin, if this is warm, the mistaken impression is given that the body is warm. In point of fact, the general temperature is lowered, owing to the increased loss from the skin. Alcohol also has been shown to lower the resistance to infection. Finally, visible changes have been found in the brain-cells of drunkards, so that there is every reason to believe that similar changes in a less degree will be produced by even comparatively small doses of alcohol. Enough has been said to show that there is no benefit of any kind to be derived from the use of alcohol. Any reason for taking it must rest on other grounds, which do not concern us here. Since this is so, if there is likely to be any shortage of food, the first prohibition to be made ought surely to be the use of materials capable of serving as food from being used in distilleries, and, to a less extent, in brew- 72 PHYSIOLOGY OE FOOD eries. For the manufacture of alcohol as a solvent for explosives, materials unfit for use as food, such as bad potatoes, can be used. There is also a large store of new whisky in the warehouses. Further information on the subject of the action of alcohol may be obtained from Cushny's Pharmacology (pp. 131-155). I cannot help expressing regret that any apology for the use of alcohol, such as that in a recent number of the Church Times should have been published. At the present time, especially, excuses for the waste in- volved in the use of alcohol should not be given. The argument that it is a " gift from God" would apply even better to opium, which is a more natural product than alcohol. It is admitted that opium should be confined to medicinal use and the same limitation should be applied to alcohol. Even for medicinal use there are better substitutes. I cannot understand how any but an ignorant person can deny that there is great waste of good food involved even in the manufacture of beer, apart from the waste of fuel and ALCOHOL 78 labour. There is always " degradation " of energy in the fermentation process. % To make potable spirit, materials useful for food, such as barley and potatoes, must be used. A religious paper should be the last to advocate what is, to put it in the most favourable light, nothing but a selfish indulgence. The head of a large sanatorium has written to me, without a request on my part, to say that he is greatly concerned about the number of cases that come to him, even of men of much value to the nation, whose efficiency is seriously impaired by the use of alcohol. From the physiological point of view, an advertisement which appeared in The Times of December 2ist, 1916, is distinctly misleading. Nothing can alter the fact that there is a loss of energy in the change from carbohydrate to alcohol. If the barley re- ferred to were consumed directly by man and cattle, the energy value obtained would be greater than if all the products resulting from its use in making beer were consumed. It is doubtless true that very little sugar is 74 PHYSIOLOGY OF FOOD added, as such, in the manufacture of beer, but the starch of the barley is converted into sugar in the process and part of its energy value lost by fermentation. So far as " tem- perance drinks " contain sugar, they have, of course, a food value ; and I fail to see where the waste, stated to exist in such drinks, occurs. As for the sixty million pounds con- tributed by the " trade " to the revenue, surely the sum available for national objects would be greater still if the consumer saved what he spends on alcoholic drinks and invested it in War Loan, while he would himself have the benefit of the investment. CHAPTER VIII VEGETARIANISM PERHAPS one of the most widely spread errors in reference to food is, that there is some special virtue in butchers' meat. Some- times it appears to be thought that there is no protein in vegetable foods. This, as we have seen, is not the case. Vegetable foods, if properly chosen, can supply all that is necessary for a complete diet. The protein is not quite so easily di- gested, but more of the food can be taken in compensation. The proper choice, however, may be the most difficult thing, since it is not an easy matter, unless some animal product, such as milk, is added. The work of McCollum, Simmonds and Pitz (1916) shows that an adequate diet for rats can be made from the three natural 75 76 PHYSIOLOGY OF FOOD vegetable foodstuffs, wheat, wheat-germ and rice. But another mixture, although con- taining a larger number of constituents, was unsatisfactory. Further, it does not follow that the mixture suitable for rats would be so for other animals or man. The conclusion drawn is that a diet of purely vegetable origin cannot be safely made up until more is known about the properties of each natural foodstuff. It is certain, on the other hand, that all the components of a successful diet can be found in foods of plant origin. CHAPTER IX EXERCISE IT has been recommended that the amount of exercise taken for pleasure should be lessened. This suggestion is made on the ground that " the need felt by many for con- stant exercise is in part due to the fact that the food eaten is in excess of what, without the exercise, would cover the needs of the body." While this may be so to some extent, uni- versal experience of the benefits derived from exercise suggests that the consumption of slightly more food may be more than compen- sated by the increase in general efficiency, The actual increase in the energy supplied by food necessitated by, say, two or three hours' exercise once a week, is a small frac- tion of the total consumption. It is to be 77 78 PHYSIOLOGY OF FOOD admitted that there is a possibility that the increased appetite resulting from exercise in the open-air may lead to a consumption of food greater than really necessary. This however, when recognized, may be guarded against. The way in which exercise produces its effects is a difficult matter to express an opinion upon. It is possible that it may be analogous to that of fresh air or a cold bath. The stimulation of peripheral nerves in an unusual manner wakes up, so to speak, the nervous system. The use of muscles, which have been more or less idle, serves also to keep in adjustment the various mechanisms of complex movements ready for every-day requirements when needed. But, while it is doubtless true that "all work and no play makes Jack a dull boy, " it is none the less true that "all play and no work makes Jack a fool." The latter part of the proverb may be commended to the devo- tees of the cult of exaggerated athleticism that one sometimes meets at the older Schools and Universities. EXERCISE 79 Of course, the remarks about muscular ex- ercise have no application to those engaged in muscular labour as their ordinary occupation. The form of recreation required by these is rather of a different kind, such as music, read- ing, etc. It is not to be supposed, however, that change of occupation of any kind is without its value to any one, whatever his regular work may be. CHAPTER X THE VALUE OF COOKING FROM what has been said above as to the destructive effect of heat on certain accessory factors of diet, it might be supposed that the process of cooking is to be deprecated. We have also seen, however, that the digestibility of some foods is improved by it, owing to the removal of certain substances which prevent the action of the digestive enzymes. Another beneficial effect of cooking is to kill micro-organisms and other parasites. But perhaps the greatest use of the art is in the preparation of dishes attractive to the palate and other senses. As we have seen, appetite plays a very important part in diges- tion, owing to the secretion of gastric juice, which is produced in the stomach, ready for the reception of food. 80 THE VALUE OF COOKING 81 The destruction of accessory factors can always be compensated for by taking fresh fruit or vegetables. The book by Kinne and Cooley (1916), although primarily intended for use in schools, will be found to contain a number of use- ful instructions, both in cookery and with reference to the preservation of food. CHAPTER XI CHARACTERISTICS OF CERTAIN ARTICLES OF DIET Sources of Protein. Meat, poultry and eggs are the most costly form of protein, even in peace times. Corned beef is cheaper, but may be deficient in accessory factors. The cheapest source of animal protein is separated milk or cheese. The cheapest vegetable source is oatmeal. It must again be insisted on that protein can be obtained equally well from either animal or vegetable source. Fish, curiously enough, when allowance is made for the large percentage of water which it contains, does not turn out to be a cheap source of protein. The cost of transport to inland towns helps to make it more costly. As regards food in general , it should be 82 CERTAIN ARTICLES OF DIET 83 pointed out that an extra price is too frequently paid for mere appearance, white rice and the cheaper grey kind are equally valuable. Special named foods made by particular firms have rarely any advantage over the ordinary market varieties. Bread. Notwithstanding the agitation some years ago by certain newspapers, it is remarkable how little difference there really is between the nutritive values of white bread and the so-called "Standard " bread. It appears that the extra protein obtained by using a larger proportion of the wheat grain than is done in white flour is comparatively indigestible. The difference is greater in some kinds of wheat than in others ; but, when allowance is made for digestibility, very little is gained. The value of the new National flour, and bread made from it, consists chiefly in the fact that a larger number of loaves can be made from the same amount of wheat without diminishing the food value. Even as much as 90% of the wheat can be made into flour, but 8% of this flour is indigestible husk. This husk has a value in avoiding constipation, 84 PHYSIOLOGY OF FOOD as pointed out above, but no nutritive value. The experience of the Food Commission in Belgium is in favour of at least 82% milling, which makes a yellowish bread. The slightly less nutrient value compared with that of 65-70% milling is more than counterbalanced by the lower cost, so that more value can be obtained for the same price. It will be re- membered that our new Government regu- lation fixes the standard of milling at 76%, which also makes a rather yellowish bread. The colour is due to the inclusion of more of that part of the grain from which the future wheat plant would grow, if the wheat were sown. It is commonly known as the germ, for this reason. Some objections have been made to the inclusion of more germ than in white flour. It is said to be more difficult to make light bread. And the flour is more inclined to be spoilt by keeping. On the other hand accessory factors are contained in the germ, although this may not be of great importance if a variety of other food is taken. The Belgian Commission point out that CERTAIN ARTICLES OF DIET 85 11% of maize flour (American corn flour) can be mixed with the wheat flour to advantage. It increases the quantity and slightly re- duces the cost per kilo (Robinson Smith, 1916, p. 7). It will be realized that the statements of some advertisers in the daily papers can only be described as misleading and mischiev- ous nonsense. It is stated, for example, that a particular bread is made from the whole of the wheat and consists of 100% of perfectly digestible material, while the Government by fixing the standard at 76% has eliminated 24% of the most nourishing part of the " berry" [sic}. This is absurd. As we have seen above, bread with the ad- dition of some fat, is a complete food in itself. Hence the popular " bread - and - butter." Speaking for myself, I would almost as readily take jam as butter, so that, at a pinch, even the fat might be eliminated. I agree also with Wood and Hopkins that we do not, in England, make sufficient use of the numerous different varieties of bread, rolls, etc. Bread may also be consumed as toast, 86 PHYSIOLOGY OF FOOD hot or cold, or with jam, butter, dripping and other things. All of these may assist in the proper appreciation of its value. Oatmeal. This is not nearly enough made use of in the South. Weight for weight, it contains more protein and more fat than wheat does. It seems difficult for the in- experienced to make good porridge. Oat- cakes are a valuable form in which oatmeal can be taken. Rice. As already mentioned, there is no advantage in using white " polished" rice. In fact, where it is the staple article of diet, the polishing removes an essential accessory factor ; so that a disease called Beri-beri results from its exclusive consumption. The Belgian Commission regards rice as the cheapest of nourishing food for the feeding of a population on a large scale. Sugar is too often regarded rather as a flavouring or sweetening agent than as one of the most valuable energy-giving foods. It should be remembered also that, as pur- chased, it consists of practically 100 per CERTAIN ARTICLES OF DIET 87 cent, available material. This refers to cane- sugar, or, what is the same, beet-sugar. In the form of treacle, it is not, of course, quite so pure. It appears that "golden syrup" consists mainly of that kind of sugar called by the chemist glucose. A preparation of this sugar, not chemically pure, is being sold for domestic purposes. There appears to be some un- deserved objection to it, apart from its flavour, which would prevent its use for some purposes. In point of fact, when we digest cane-sugar, half of it is converted into glucose. Possibly there may be an idea that commercial glucose is not sugar at all. The sugar present in fruits is glucose, while that in the reserve depots of the stem and root is cane-sugar, or saccharose, to give it the chemical name. Glucose is not so sweet as saccharose. The chemical compound known as " sac- charin " is not a foodstuff, and must not be supposed to be a substitute for sugar. Fresh Fruit and Vegetables. The chief 88 PHYSIOLOGY OF FOOD value of these consists in accessory factors. In the East End of London the only fresh vegetable food used by the majority of the poorer population is fruit, and mainly oranges. We see, from this fact, the justification of the protests raised against the restriction of the import of oranges. Milk. This, as remarked already, is one of the cheapest sources of protein, actually the cheapest source of animal protein. Wood and Hopkins point out the waste involved in not making more use of separated milk for human food, but its bulk involves diffi- culties of transport. At a time when 1000 calories in the form of meat cost one shilling, the same amount could be obtained from milk at a cost of fourpence three-farthings. Condensed milk is not economical. Butter and Margarin. While butter is the most digestible form of fat, margarin may well take its place for most purposes. The only objection to the better qualities r i_ i ? "r ^^--vK t of margarin is their lack of taste. But this is preferable to the objectionable taste of the CERTAIN ARTICLES OF DIET 89 inferior qualities. Whether this is due to an attempt to imitate the taste of butter, or to something present in the raw materials, I do not know. Whatever it is, it would be better absent. CHAPTER XII POSSIBILITIES OF ECONOMY IN order to obtain some idea how economy might be effected, it will be instructive to examine some typical family budgets. I take these from the data given in the book by Wood and Hopkins. They rest upon careful measurements of actual consumption, and may be taken as representative of the state of things before the War. Taking, in the first place, the case of fourteen families in York, as investigated by Mr. Rowntree. The average income of these particular families was less than 265*. per week. Their average consumption, per " man," was 2685 calories, and the pro- tein in the diet amounted to 89 grams. All that may be remarked about this diet is that the energy value is undoubtedly low, 90 POSSIBILITIES OF ECONOMY 91 and that better value might possibly have been obtained at the same expense if part of the protein had been replaced by carbo- hydrate. But there is the uncertainty as to how large a proportion of the individuals might have been growing children, who would require more protein than the adults do. Next, let us take a family with a higher income, that of a foreman earning 385-. a week. The food consumption per "man" amounted to 145 grams of protein and 4800 calories. The details of the budget will be found in Wood and Hopkins, and it would seem that some diminution both in protein and energy value could be effected without detriment, especially in protein. Passing on to an income of ^150 to 200 a year, the values are 140 grams protein, 4250 calories. A further case is that of a family keeping three servants. Here the values are 143 grams protein, 4379 calories. On this last case, Wood and Hopkins remark that the total food might be reduced by one-sixth and part of 92 PHYSIOLOGY OF FOOD the meat consumed might be replaced by cheaper sources of protein, such as bread or oatmeal. They conclude that, while the poorer classes cannot make any retrench- ment in food expenditure, the wealthier classes might save 10 per cent, of the whole national expenditure on food. This saving would amount to at least sixty million pounds per annum, no mean figure. It is interesting to compare the amount of food obtained for one shilling by different classes of the population before the war : Labouring Class. Artisan. Wealthy. Protein . . . 179 140 92 Calories . . . 5500 4250 2850 The conclusion to be drawn from this table is that those who have been accustomed to consume their protein in the form of meat might advantageously replace part of it by the cheaper vegetable sources of protein. It might not perhaps be advisable to replace the whole of it : the 4 oz. standard might be divided up somewhat as follows POSSIBILITIES OF ECONOMY 98 i oz. as meat. 1 oz. as milk. 2 oz. as oatmeal, bread or beans. The actual necessary amount of food is less than is usually supposed, if we take the food budgets of the wealthier families given above as an index of the general practice in such cases. It must be admitted that it is a matter ot some difficulty for any household to work out with any degree of accuracy what its consumption is. It can probably be esti- mated most easily by averaging the purchases of food during a period of several days, the longer the better, and calculating their value from Miss McKillop's tables (1916). The work will be found by no means devoid of interest. But the real " man value " of a household is a matter of some uncertainty. Certain members' take lunch away from home, and friends or relatives on leave come in at various times. With a little trouble, how- ever, these factors can be given their due arithmetical weight, without much inaccuracy. 94 PHYSIOLOGY OF FOOD In a household of few persons, it is naturally a simpler process, but the result would prob- ably be more subject to the errors incident to individual peculiarities. The wealthier classes, however, apart from any calculation, may take it that they may, without any dis- advantage or risk, attempt to reduce their expenditure on food by one-sixth in some cases by replacing expensive articles by cheaper ones, in other cases by diminution of quantity. It is probable that a diminution in the daily ration would, at first, be attended with some degree of discomfort, but benefit would soon be felt. The main object of the present book is to show that it can be done without risk to health. Those who wish to economize for patriotic reasons will be ready to accept the small initial discomfort the more easily when they are satisfied that no harm will result. It has been noticed that Irish peasants, used to the consumption of voluminous rations of potatoes, have complained of hunger, and even of starvation, when given food of greater value, but of smaller bulk. POSSIBILITIES OF ECONOMY 95 Similarly, Bavarian peasants, used to bread, complain if given a diet of meat. The change of any habit is apt to cause at first a feeling of want, which disappears sub- sequently. Some old observations show how ancient habits with regard to consumption of food are adhered to. I refer to Dutch settlers in Java, whose consumption of food was found to be the same as in Holland, although the conditions of a tropical climate imply that less is required. One of the most pressing needs at the present time is a control of the prices of food and a means of ensuring equality of distribu- tion, the latter especially in the case of sugar. Many dealers in foodstuffs appear to think themselves justified in exacting as high a price as they can get their customers to pay. The experience of the Food Commission in Belgium suggests that prices are unnecessarily high here in England, particularly in the case of bread. A reduction in the consumption of food is probably only to be obtained, to any notable extent, by the voluntary efforts of patriotic 96 PHYSIOLOGY OF FOOD citizens. Attempts at control from outside do not promise well, if we may judge from the results of the recent limitation of meals in restaurants. The effect of this has been, so far as we can see, to increase the consumption of meat and to decrease that of sweets, precisely the opposite of what is desirable. We must, however, all of us assist the Food Controller in his very difficult task by cheer- ful acceptance of the conditions which he feels it necessary to impose. No doubt, suggestions made with the desire to help, and not to find occasion for carping criticism, will be met with welcome and receive careful consideration. CHAPTER XIII GENERAL CONCLUSIONS BY way of summary, we may conclude with the aphorism already given " Take care of the calories and the protein will take care of itself " But we must also remember that the number of calories really necessary is by no means so great as it is frequently imagined to be. The accessory factors, again, like the pro- tein, do not, as a rule, require special considera- tion. At the same time, it is well to ensure their presence by taking fresh fruit or salad. These are practically the only uncooked food taken in this country, with the exception of milk. Oysters can scarcely be regarded as a regular article of diet. H 97 98 PHYSIOLOGY OF FOOD With respect to the substitution of a part of the animal protein, usually taken, by its equivalent in the vegetable form, it is of some importance to refer to what has been pointed out in connection with the use of farm land. It appears that more food per acre can be obtained by growing wheat than by using the land as pasture for sheep or cattle. There are, doubtless, economical reasons why the farmer hesitates to make the change, but the fact must be kept in mind. As to the necessity for economy in the use of wheat and other cereals, the Report of the International Institute of Agriculture in Rome, with regard to the crops of 1916, is to be considered with care. The wheat crop of 1916 turns out to be only 93*4% of the average ; but there are remainders from 1915, which was an exceptionally good year. There are also to be added some crops from the Southern Hemisphere reaped in December and Janu- ary. On the other side, the Report points out that there is likely to be an increase in consumption owing to improvements in eco- nomic conditions, movements of population, GENERAL CONCLUSIONS 99 arrival of armies, increase of rations to mo- bilized units, etc., and the conclusion is drawn that " considerable drafts upon the remainders mentioned must be made in order to bridge over the interval " up to the harvest of 1917. "It is therefore both urgent and indispen- sable to effect serious economies in consump- tion. Otherwise available supplies at the end of the current season would be much reduced and might even be insufficient if next harvest should not prove to be a plentiful one." It may be well to refer, finally, to the fact that no attempt has been made in this manual to deal with special food required in disorders of nutrition. That is the province of medical science, which deals with the diseased organ- ism, while physiology deals with the activities of the normal healthy organism, plant as well as animal. Physiology is thus the foundation not only of medicine, but of hygiene and also of agriculture. I call attention to this be- cause it is sometimes thought that a know- ledge of physiology is only necessary for the student of medicine. Since it deals with the normal activities of our bodies as they are H 2 100 PHYSIOLOGY OF FOOD used every day, it should be obvious that some knowledge of it is of vital importance to all of us and ought to be possessed by all of us. One of the problems of physiology is that of food, and an elementary account of this problem has been ' attempted , in the preceding pages. REFERENCES BAYLISS, W. M. (1916). Principles of Gen- eral Physiology. Longmans, 2 is. BENEDICT, F. G., and E. P, CATHCART (1913). Muscular Work. Publication of the Nutrition Laboratory, Carnegie Institution of Washington. No. 187. CARLSON, A. J. (19 1 6). The Control of Hunger in Health and Disease. Univ. of Chicago Press, and Cambridge Univ. Press. 9^. CATHCART, E. P. (1912). The Physiology of Protein Metabolism. Longmans. Commission for Relief in Belgium. First Annual Report (1916). 3 London Wall Buildings, E. C. COOK, CAPTAIN JAMES (1776). The Method taken for Preserving the Health of the Crew of His Majesty's Ship, the "Reso- lution" during her late Voyage Round 101 102 REFERENCES the World. Phil. Trans. Royal Society. 66, 402-406. CUSHNY, A. R. (1910). Textbook of Pharm- acology and Therapeutics. Philadelphia: Lea and Febiger. 5th Edn. FISHER, IRVING (1905). A New Method for Indicating Food Values. Amer. Journ. Physiol., 75, 4I7-43 2 - HAMILL, J. M. and S. B. SCHRYVER (1916). Nitrogenous Metabolism in Normal In- dividuals. Proc. Physiol. Soc. in Journ. Physiol. j^, pp. x-xii. HINDHEDE, M. (1913). Studien ueber Ei- weissminimum. Skand. Arch. Physiol., 30, 97-182. KINNE, HELEN and ANNA M. COOLEY( 16^16). 7 Food and Health. Home- Making Series. New York : The Macmillan Co. 3^. LANGWORTHY, C. F. (1908). Food and Diet in the United States. Year- Book of the United States Department of Agricul- ture, 1907. Washington, 1908. LUSK, GRAHAM (1909). The Elements of the Science of Nutrition. Saunders, London and Philadelphia. 125*. 2nd Edn. REFERENCES 103 McCoLLUM, E. V., and MARGUERITE DAVIS (1915). The Essential Factors in the Diet during Growth. Journ. Biol. Chem. 23, 231-246. McCoLLUM, E. V., N. SIMMONDS, and W. PITZ (1916). The Vegetarian Diet in the Light of our Present Knowledge of Nutrition. Amer. Journ. Physiol., 41, 333-360. (1916). The Distribution in Plants of the Fat Soluble A, the Dietary Es- sential of Butter Fat. Amer. Journ. Physiol. 41, 361-375. McKiLLOP, MARGARET (1916). Food Values, What they are and How to Calculate Them. Routledge. is. PAVLOV, I. P. (1910). The Work of the Digestive Glands. Trans, by W. H. THOMPSON. Griffin. 2nd Edn. ROWNTREE, B. S. Poverty, a Study of Town Life. Macmillan. 2s. 6d. SMITH, ROBINSON (1916). Food Values and the Rationing of a Country. Commis- sion for Relief in Belgium. 3 London Wall Buildings, E. C. 104 REFERENCES STARLING, E. H.(i9i6). Principles of Human Physiology. Churchill, 2is. 2nd Edn. THOMPSON, W. H. (1916). The Food Value of Great Britain's Food Supply. Eco- nomic Proc. of Royal Dublin Society. 2, 168-220. WOOD, T. B. (1916). The Story of a Loaf of Bread. Cambridge Univ. Press. is 6d. WOOD, T. B., and F. G. HOPKINS (1916). Food Economy in War Time. Cam- bridge Univ. Press. 6d. INDEX Accessory factors, 56, 97 ; in plants, 60 Affinity, chemical, 13 Alcohol, 67 ; effect of, on digestion, 64 Amino-acids, 16 Appearance of foods, price paid for, 83 Appetite, 62, 63, 80 Arrowroot, 65 Athleticism, 78 Belgian Food Commission, 39 Beri-beri, 58 Bitters, 64 Bread, 43, 83 , Composition of, 43 , " National," 83 , "Standard," 83 Butchers 1 meat, 75, 82 Butter, 42, 43, 88 Calculation of food consump- tion, 93 Calorie defined, 21 Carbohydrate, value of, 50, 52, 55 Carbohydrates, chemical nature of, 29 Carbon compounds, 12 dioxide, 14 , peculiarities of, 13 Carbonic acid, 14 Change of habit, 94, 95 Cheese, 42 Chemical affinity, 13 Cold bath, 24 weather, 33 Condensed milk, 88 Conservation of energy, 9 Constituents of the body, n Control of meals, 96 ; of prices, 95 Convertibility of energy, 18, 19 Cooking, 54, 80 Custard, 65 Diabetes, 52 Digestibility, 61 Digestion, 17, 53 Disorders of nutrition, 99 Economic aspect of food problem, 3 Economy, possibilities of, 90,94 Economy in use of cereals, 9 8 Efficiency of animal ma- chine, 33 Eggs, 42 , raw and cooked, 64 Energetics, first law of, 9 , second law of, 20 Energy and work, 8 conservation of, 9 105 106 INDEX Energv, convertibility of, 18, 19 defined, 8 of the sun's rays, 1 5 , transfer of, 19 Enzymes, 60 Exercise, 24, 77 Farm land, use of, 98 Fat-soluble A factor, 59 Fats, chemical nature of, 28 , value of, 52 Fermentation, 73 Fish, 42, 82 11 Flesh formers," 23 Food budgets, 90 stuffs, classes of, 30 supply of England, 37 Fresh air, 23 Fruit, value of, 60, 87 Gastric juice, 62 Gelatin, 65 Germ of wheat, 84 Glucose, 87 " Golden syrup," 87 Gout, 52 Green plant, 15 Growth, 6 and maintenance dif- ferent, 1 8 Heat energy, 20, 21 " Heat formers," 23 Hunger, 63 Hygiene, 99 Indigestible matter, function of, 30 Life as transfer of energy, 19 Maintenance 6 Maize, added to bread, 85 " Man value" of population, 36 Margarin, 88 Meat extracts, 64 Mental work, energy con- sumption of, 34 Milk, 42, 82, 88 Minimum of protein, 44 Muscle, food of, 45 Mutton, 42 " National" bread, 83 Nitrogen compounds, 7, 15, 16, 18 Nuts, protein of, 61 Oatmeal, 42, 43, 82, 86 Oranges in East London, 88 Oxygen as food, 23 Peas, 42 Petrol motor, 10, 12, 18, 26 Physiology, scope of, 99 Possibilities of economy, 90, 94 Potatoes, 43, 47 Poverty, 48 Products of protein meta- boles, 51 Protein food, use of, 25, 26, 49; minimum, 44 , chemical nature of, 16 of nuts, 6 1 , sources of, 82 Recreation, 79 Regulation of prices, 39 Rice, 86 Saccharin, 87 Salts, 12 Scurvy, 58 Soup, 64 Sources of protein, 82 INDEX 107 "Specific dynamic energy," 49 ''Standard "bread, 83 Standard diet," 32 Steak, 42 Stomach, digestion in, 54 Sugar as food, 42, 43, 55, 86 Temperature, effect of alcohol on, 71 Thermodynamics, 20 Triangles of food values, 44 Urea, 51 Uric acid, 51 Use of farm land, 98; of food, 6 Value of cooking, 54, 80; of particular food stuffs, 42 Vegetarian diet, 75 " Vitamines," 56 War rations, 37 Wasting disease, 65 Water, 12 soluble B factor, 59 Wear and tear, 6, 18 Wheat crop of 1916, 98 Work, 7 PRINTED IN GREAT BRITAIN BY RICHARD CLAY & SONS, LIMITED, BRUNSWICK ST., STAMFORD ST., S.E., AND BUNGAY SUFFOLK. 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