Flour is made from cereals and from other seeds by removing the husk and grinding the remainder. The best wheat flour is made from the white interior of the wheat grains, and contains the greater proportion of the starch of the grain, and most of the proteid. Whole flour is made from the whole grain minus the husk, and thus contains not only the white interior, but also the harder and browner outer portion of the grain. This outer region contains a somewhat larger proportion of the proteids of the grain. Whole flour thus contains 1 to 2 per cent. more proteid than the best white flour; but it has the disadvantage of being less readily digested. Brown flour contains a certain amount of bran (the coating of the grains) in addition; it is still less digestible, but is useful as a mild laxative, the insoluble cellulose mechanically irritating the intestinal walls as it passes along.

The best flour contains, or should contain, little or no sugar. The presence of sugar indicates that germination has commenced in the grains. In the manufacture of malt from barley, this is purposely allowed to go on.

mass.

Wheat flour when mixed with water forms dough, a sticky, adhesive This is due to the formation of gluten; and the forms of grain which are poor in gluten cannot be made into dough or bread (oats, rice, &c.). Gluten does not exist in the flour as such, but is formed on the addition of water from the pre-existing globulins (Martin; see more fully p. 135).

Bread is made by cooking the dough of wheat flour mixed with yeast, salt, and flavouring materials. The yeast acting at the commencement of the baking, when the temperature of the oven is little above that of the body, forms sugar and dextrin from the starch, and then the alcoholic fermentation occurs. The bubbles of carbonic acid burrowing passages through the bread make it light and spongy. This sponginess enables the digestive juices subsequently to soak into it readily, and affect all parts of it. In the later stages of baking, the gas and alcohol are expelled from the bread, the yeast is killed, and a crust forms from the drying of the outer portions of the mass of dough. Other methods have been, or are, adopted for making dough light; the

leaven of the ancients was a piece of putrid dough; baking powders are mixtures containing sodium bicarbonate, from which the carbonic acid is driven off during baking. White bread contains in 100 parts, 7 of proteid, 55 of carbohydrates (starch, dextrin, and sugar, the two last more abundant than in the flour), 1 of fat, 2 of salts, and the rest water. An adult would require daily about 1·6 kilo. of bread to supply him with the requisite amount of proteid ; this would, however, contain an overdose of carbohydrate.

Leguminous plants.-The meal of peas, beans, and lentils are rich in proteids, and are used by vegetarians as substitutes for meat. Potatoes are chiefly starchy. The percentage composition of the foods just mentioned is given in the following table:

It has been calculated that 4-5 kilogrammes of potatoes would be necessary daily to supply an adult with the requisite amount of proteid; a bulk far too great for an ordinary alimentary canal to manipulate. In fact, unless a vegetarian diet is supplemented by some concentrated form of proteid, like milk, eggs, or cheese, it will be found impracticable, and the person who takes it will waste. Fermentative changes occurring in the alimentary canal, and giving rise to gases (carbonic acid, marsh gas, &c.) from the starch and cellulose, give rise to flatulence, which is a most serious drawback to vegetarianism.' Rice has not this particular disadvantage to such a marked extent.

It is well known that the inhabitants of certain countries (e.g. the coolies of India) are able to subsist on a smaller quantity of nitrogenous food than the average European. Recent experiments have shown that even Europeans can train themselves, gradually, to maintain bodily equilibrium for short periods on less than the fifteen grammes of nitrogen daily which has been hitherto supposed to be necessary. The disadvantages of pure vegetarianism resulting from overloading the stomach and flatulence remain, however, unaltered. Looking at the table just given, it is seen that beans contain rather more nitrogenous material than beef but experiments on man have shown that beans are a most 1 See Rutgers, Zeit. Biol. xxiv. 351. 2 F. Hirschfeld, Pflüger's Archiv, xli. 533.

:

unsuitable form of food when taken exclusively. It cannot be too often repeated that the digestibility of a food, as well as its percentage composition, must be taken into account in estimating its nutritive value. Prausnitz' experiments with beans gave the following results: The fæces contained 18.3 per cent. of the food weighed as dry material, and 30-3 per cent. of the nitrogen undigested. Beans thus compare most unfavourably with bread, lentils, and other forms of vegetable food.

Green vegetables.--These are taken as a palatable adjunct to other foods, rather than for their nutritive properties. Their potassium salts are, however, abundant. Cabbage, turnips, and asparagus contain 80 to 92 water, 1 to 2 proteid, 2 to 4 carbohydrates, and 1 to 15 cellulose per cent. The percentage composition of the green foods of herbivora have been already given (p. 573), and the small amount of nutriment they contain accounts for the large meals made by, and vast capacity of the alimentary canal of these animals.

Accessories to Food

Alcohol.--Small quantities of the alcohol taken leave the body by the breath and urine as such; the greater amount is decomposed into simpler products (acetic, oxalic, carbonic acids, and water); the forma tion of these must give rise to a certain amount of bodily heat. It has been calculated that a man can burn off in his body two ounces of absolute alcohol daily. Alcohol is thus within narrow limits a food. It, however, lessens proteid metabolism by about 6 per cent., and thus ultimately leads to a diminution of the heat produced in the body. It is, moreover, a very uneconomical food; much more nutriment would have been obtainable from the barley or the grapes from which it was made. The value of alcohol used within moderate limits is not as a food, but as a stimulant, not only to digestion, but to the heart and brain. The percentage of alcohol in liquors is as follows: Spirits, 50 to 60 or 65; port and sherry, 16 to 25; clarets and champagne, 5 to 13; porter and Bass' beer, 8 to 10; light beers 2 to 5. Various liquors are differently coloured and flavoured; some, like hocks, are acid; others are sweet from the presence of sugars and glycerine; port abounds in tannin, sherry and brandy in various ethers and alcohols; some, like champagne, are sparkling from excess of carbonic acid. Malt liquors contain bitter and other principles from the hop.

Condiments, like mustard, pepper, ginger, curry powder, are stomachic stimulants. Their abuse is followed by dyspeptic troubles.

1 Zeit. Biol. xxvi. 227.

2 The reader interested in the subject of alcohol in diet should read Chapter VIII of Bunge's Physiol. Chem. (transl. by Wooldridge).

(Tea, coffee, and cocoa. These are stimulants chiefly to the nervous system. Tea, coffee, mató (Paraguay), guarana (Brazil), cola nut (Central Africa), bush tea (South Africa), and a few other plants used in various countries, fall owe their chief property to an alkaloid called theine or caffeine' (C,H10N4O2+H2O); cocoa to the closely related alkaloid, theobromine (C-H,N,O2); coca to cocaine. These alkaloids ( are all poisonous, and, used in excess, even in the form of infusions of tea and coffee, produce over-excitement, loss of digestive power, and other disorders well known to the practical physician.Coffee differs from tea in being rich in aromatic matters; tea contains a bitter principle, tannin; to avoid the injurious solution of too much tannin, tea should only be allowed to infuse (draw) for a few minutes. Cocoa is a valuable food in addition to its stimulating properties, containing about 50 per cent. of fat and 12 per cent. of proteid.

I have not attempted to give references to the vast amount of literature published on the subject of alcohol. A few of the more recent papers on the subject will be found referred to in the chapter on alcohol in Bunge's book. I am indebted to the same book for the following references to papers on the constitution and physiological action of caffeine and allied alkaloids. Caffeine is trimethylxanthine (i.e. xanthine with three methyl groups introduced into its molecule), and can be prepared artificially (E. Fischer, Liebig's Annalen, ccxv. 253). Theobromine (the alkaloid contained in cocoa, and mixed with caffeine in guarana) is dimethylxanthine. Mono-methylxanthine is at present unknown. The physiological action of this series of substances has been studied by Filehne (Du Bois Reymond's Archiv, 1886, p. 72), and Kobert (Arch. f. exp. Path. u. Pharm. xv. 22).

CHAPTER XXVII

DIET

A HEALTHY and suitable diet must possess the following characters : 1. It must contain the proper amount and proportion of the various proximate principles-proteids, fats, carbohydrates, salts, and water.

2. It must be adapted to the climate, age, and sex of the individual, and to the amount of work done by him.

3. The food must not only contain the necessary amount of elements, but these must be present in a digestible form.

The subject of diet is necessarily related to that of excretion. The object of the food is to repair the waste of the body; the amount of waste or loss must be known before the amount necessary for repair can be ascertained. The varying relations between income and expenditure, and the balancing of the two sides of the sheet, cannot here be conveniently studied in detail, but after our consideration of the urine and other excretions, we shall be then better able to consider the exchange of material or metabolism of the body in relation to nutrition. For the present we must content ourselves with stating very briefly the principles on which diets have been constructed, and this we can do most readily under the three heads enumerated above.

The relation between the proximate principles in a diet.-We have seen that a proteid contains carbon, hydrogen, oxygen, nitrogen, and sulphur, and it might be said that proteid plus water and mineral matter would supply a man with all the materials he wants, and the question will be asked, what is the use of the fats and carbohydrates, which only contain carbon, hydrogen, and oxygen? If we examine the materials that leave the body, we shall obtain an answer to this question. A man doing a moderate amount of work will eliminate, chiefly by the lungs in the form of carbonic acid, from 250 to 280 grammes of carbon per diem. During the same time he will eliminate, chiefly in the form of urea in the urine, about fifteen to eighteen grammes of nitrogen.'

In order to repair this loss, the daily food should contain, roughly,

1 In addition about six grammes of hydrogen, and 700 grammes of oxygen, and thirty grammes of salts are parted with, but the dietetic value of a food depends chiefly on the amount of carbon and nitrogen it contains.