The kind of food would imagine that if a meal were set down to a man consisting of so many ounces of carbon (char coal), so many ounces of hydrogen gas, so many of nitrogen gas, and so ninny of oxygen, he would have all that was required to maintain his strength. But man, in common with other animals, is unable to take the elements, the raw elements, in this way, and make use of them. He needs to have the elements put into combinations that will suit his peculiar organi zation. Plants are able to take the elements up, however, and transform them into the living substance of their own bodies. Plants combine them, that is to say, for the benefit of man and the rest of the animal kingdom ; and then men and animals make use of plants for food—corn, wheat, barley, potatoes, and so on,— and so obtain the elements in a combined state which they could not make use of in the simple state. So that the question comes to be, is there a substance containing the four elements named which man can use as a food to repair the waste of his tissues? There is a class of substances, called Proteids, which contain all four elements, carbon, hydrogen, oxygen, nitrogen. They are also called albuminous substances, because a type of the class is albumin — white of egg. Belonging to the same class is a substance called gelatin, obtained by boiling tendons and con nective tissues, another called chondrin, yielded by boiling cartilage (gristle). Another of the class is found in flour, called gluten; and in peas or beans is still another, legumin. The curd of milk, from which cheese is made, con sists mainly of an albuminous body—casein, and from flesh is found another of the class, namely, myosin. So that all four elements one could obtain from a quantity of white of egg, curd of milk, or meat. So one might well ask the question, since an albuminous body con tains all the required elements, can a man not live on, for example, white of egg alone, or lean meat alone, or a diet of beans or peas alone? Well, an American physician, Dr. Hammond, in 1857 tried some experiments on himself, and limited himself to 1 lb. of albumin daily, with 4 lbs. of distilled water. On the fourth day he began to experience loss of appetite, headache, and weakness. His disgust at the perpetual sameness and tastelessness of the diet became almost unbearable, and on the ninth day, after severe diarrhoea, he had to give it up. Now, this is not to be wondered at, considering the tastelessness of the diet ; but albumin might be made to form the chief portion of the diet, but might be given in a much more palatable form, and might be varied—white of egg one day, lean meat another. Still the attempt to live on an albuminous diet alone would be very difficult to accomplish, for a reason that will now be given. The total quantity of nitrogen cast out of the body daily by a man under ordinary circumstances is 300 grains, of carbon about 5000 grains. The quantity of hydrogen and oxygen cast out are replaced by oxygen obtained from the air he breathes, of which he will take into his body by his lungs about 2 lbs. weight daily, and by water, which contains oxygen united with hydrogen, of which 60 to 70 oz. per day are sufficient. Thus, supposing a man to have pure air to breathe and water to drink, he requires 300 grains nitrogen and 5000 grains carbon; that is, 15 grains of car bon for every I of nitrogen. In albumin, however, the proportion of nitrogen to carbon is 1 to 31, instead of 1 to 15, which is as much as to say that a man who sought to live on albumin would get in his food a proportion of 1050 grains (instead of 5000) of carbon for every 300 of nitrogen. In other words, in order to secure his 5000 grains of carbon he would require to take a quantity of albumin that would yield him that amount. But this quantity yields also 1428 grains of nitrogen, which are 1128 more than he requires. So that to live on albumin alone he needs a quantity that gives him far too much nitrogen, for which he has no use, and which casts labour on his body to get rid of the excess. To take an example, one would require to eat 4 to 5 lbs. of lean meat to get 5000 grains of carbon, while 1 lb. will yield the required nitrogen. To eat 5 lbs. of meat would mean immense unneces sary labour cast on the digestive organs. Only an albuminous body, however, will yield nitro gen in a condition to be made use of by man, and we are, therefore, face to face with the next problem : is there any other class of foods which could be mixed with the albuminous so as to get the required carbon and nitrogen in the most economic way? The class of food stuffs to which fat belongs contains carbon, hydrogen, and oxygen, without any nitrogen, and a class called amyloid or carbohydrates, to which sugar, starch, and gum belong, contains the same three elements without any nitrogen. We thus see that by taking a quantity of lean meat or white of egg just sufficient to supply 300 grains of nitrogen the addition to it of a certain quantity of sugar, starch, or fat will provide the necessary carbon without increas ing the nitrogen. Or, to take a better example, bread contains carbon in the shape of sugar and starchy matters, and albumin in the shape of the gluten of the flour. It has all the re quisite elements, therefore, but in it the quan tity of nitrogen is small in comparison to the quantity of carbon. Enough carbon could be obtained out of 2 lbs. of bread, but this quan
tity would yield only half the amount of Intro gen, so that 4 lbs. of bread would be required to yield a sufficient amount of nitrogen, and that would contain double the carbon necessary. Thus bread has the carbon in abundance, but is deficient in the nitrogen, and lean meat has the nitrogen in abundance but is deficient in the carbon. Unite the two, and you have as a result that 2 lbs. of bread yield very nearly the required amount of carbon and half the required nitrogen, and lb. of lean meat yield the other half of the required nitrogen and a small quantity of carbon, sufficient to swell that obtained from the bread to the full amount re quired. A combination, then, of two different kinds of food-stuffs, in proper proportions, yields the required substances for repairing the waste of the body, while it throws the least possible amount of work on the body for their digestion. In this consists the economy of a mixed diet. One of the most admirably pro portioned of human diets is milk, which con tains albumin in the form of curd (casein), that is the nitrogen, and the carbon in the form of fat (the cream) and sugar (the sugar of milk). These are dissolved in water, all in due pro portion, and thus we have a type of a food fitted not only by its ingredients for the nour ishment of the body, but by its form for easy and rapid digestion and passing into the blood.
It is now necessary to remark that there are cast out of the body, besides substances con taining the four elements mentioned, other substances belonging to the mineral kingdom— saline bodies, chief of which are salts of soda and potassium, and particularly chloride of sodium (common salt). These must also be replaced. Bread invariably contains such salts, so also does milk, meat as well.
To sum up, then, we see that to replace waste there must be introduced daily into the body a certain quantity of water, a certain quantity of solid food containing albumin, and fat, or starch, or sugar, and a small proportion of saline material, and a certain quantity of oxy gen gas taken in by the lungs. The quantity of water has already been stated as between 60 and 70 oz. daily, and the quantity of solid food ought to be 28 oz. This is the least quantity that is consistent with maintenance of vigour for an ordinarily healthy man doing an average amount of work.
[For information about the nourishing quali ties of various sorts of food, and accessory food factors or vitamins, refer to Vol. 11., pp. 100, 141.] The destination of purpose of food, it has been seen, is to repair the waste going on continually in the body. The waste occurs iu no one part in particular, but in all the tissues of the body. The contraction of a muscle necessary to move a limb means the using up of some portion at least of the fibres of muscle, the waste, that is, of sonic of the elements which go to make up the contracting muscle. The beating of the heart means the same thing, the perpetual consumption of sonic of the particles which go to make up the heart's substance. The activity of the liver means the constant breaking down of the small cells of which the liver is composed. Thinking, feel ing, willing, imagining, in the same way are all attended by the waste of nervous tissue. So it is with every organ and tissue of the body. For a more detailed discussion of this fact read the "Story of a Muscle in Action ", p. Every one of these tissues comes into direct contact with the blood. Every organ has its blood supply conveyed to it by vessels large or small according to the size and activity of the organ. The blood-vessel has no sooner entered into the organ or tissue than it breaks up into a number of branches, which in turn send off countless tiny streams that How through the tissue, pervading it in every direction. As a result the ultimate cells or fibres which form the tissue are constantly bathed by the streams that continually flow past them, The cells and Three are continually wasting, and the stream A blood as continually brings to them the means of repair. It offers to them the raw material needed for their continued industry ; rind they are able to select from the passing current whatever they require to repair their waste and to provide for their renewed activity. At the same time, as the current goes past it is a convenient channel for the removal of the products of waste, that must not be allowed to remain in the tissues. The waste, then, occurs in the tissues, the means of its repair are ob tained from the blood. In the end it is the blood that is impoverished. From it the drain of nourishment takes place. So long as it is of proper strength and in proper quantity the re newal for the wasted tissues is provided. So that due provision is made for the nourishment of the tissues if a proper condition of the bleed is maintained. Thus the food we take is first of all directed to renewing the blood and main taining its efficiency. While, then, the purpose of the food is for the repair of waste, its imme diate destination is the blood. How does it get there? is naturally the question. It must pass into the blood-vessels out of the cavity of the stomach and the canal of the intestine; but how? There are no visible openings communi cating with this canal on the one hand and the blood stream on the other. There is no vessel or chaunel which acts as a medium of communi cation between the two.