c. If the clear liquor from which the| The soft parts of the body, indeed the starch has subsided be brought to a boil on entire combustible part, consists essentially the fire, white curdy flocks will separate of three substances, or, more correctly, of and fall to the bottom. From its close re- three groups of analogous substances. semblance to boiled white of egg-the albumen of chemists-this white matter has been called vegetable albumen. d. If, after the separation of these flocks, the water be evaporated to dryness, a little sugar and gum will remain behind; while if the gluten, obtained as above described, be boiled in ether, a portion of fatty oil will be extracted. mal body. a. The cellular substance, which pervades and forms the outline of the whole body. When the skins of animals are boiled, a jelly is obtained, to which the name of glue is usually given; by chemists it is called gelatine. When the cartilages of young bones are boiled, they also yield a jelly, differing in some degree from the former, and to which the name of chondrin is given. In e. If oatmeal or beanmeal be intimately a solid state, these compounds form the mixed with water, and then allowed to substance of the cells and vessels of the anistand till the starch settles to the bottom, the addition of vinegar to the clear liquid b. The muscular fibre, which forms the will throw down a curd, having much re- fleshy parts of the body. If a piece of fresh semblance, in properties and composition, lean mutton or beef be washed for a length to the curd of milk. As its composition of time in a stream of water, the blood will has not as yet been exactly made out, the provisional names of avenine and legumin are given to the substances thus obtained from the oat and the bean respectively. They serve the same purpose in these seeds as the gluten does in the grain of wheat. Thus the organic part of plants consists essentially of four classes of substances, The cellular substance or woody fibre, Gluten, albumen, avenine, legumin, The first of these is composed of carbon (pure charcoal) and water only, and forms from a fourth to a half by weight of all our cultivated crops in their dry state. The starch group consists also of carbon and water only, though in different proportions. It forms from one-half to three-fourths of the weight of all the kinds of vegetable food on which we usually live. The gluten group is distinguished by containing about fifteen per cent. of nitrogen, with a small proportion of sulphur or phosphorus, or both. In wheat it forms about one-tenth, in oatmeal nearly a fifth, and in beans often as much as a fourth of the whole weight. The fats contain no nitrogen, and, in our cultivated grains, vary from one per cent. to ten per cent. of the whole; in our oily seeds they sometimes amount to one-fourth of their weight. The animal eats all these substances mixed together, in its vegetable food; it lives upon, and is nourished by them. What purposes do they respectively serve in the animal economy? To understand this, we must first study the composition of the organic part of the body itself. be removed, and a white fibrous substance will remain, which is the pure fibre of the muscle, more or less mixed with fat. The white of the egg, (albumen,) and the pure curd of milk, called by chemists casein, are analogous to muscular fibre. They are all analogous, also, to the gluten and legumin of wheat and other grains, and, like them, contain fifteen per cent. of nitrogen, and a little sulphur or phosphorus, or both. c. The fat, which, in an animal in good condition, forms nearly one-third of the weight of the soft parts of the body. It is very analogous-in some cases absolutely identical-with the fatty matter of the vegetable food. It will be useful now to compare together the constitution of the organic parts of the animal and the vegetable respectively. The plant contains- The animal contains 1. Cellular substance, 1. Cellular substances. or woody fibre. Gelatine, chondrin. 2. Gluten, albumen, &c. 2. Fibrin, albumen, &c. 3. Fatty matters. 3. Fatty matter. 4. Starch, gum, sugar. This comparison shows us, that in both animals and vegetables there is a cellular substance performing analogous functions in each, though of unlike compositionthat in both there are substances, gluten and fibrin, which are almost identical; the fats, which are often absolutely identicaland that the only marked difference beween them consists in the large quantity of starch, &c., which is present in vegetable food. We can now understand what are the functions which the plant has to perform in reference to animal life, and what purposes are served by the several constituents of the vegetable food which we eat. upon animal food; still fewer the diet of which might not occasionally be improved by a judicious admixture of substances of animal origin.* Thus as to the duty of the plant, we formerly saw, that one of its purposes was to draw from the soil those mineral, saline, The gluten of the plant and the muscular or inorganic substances which are neces- fibre of the animal are almost identical, and It may sary to form the harder parts of the animal yet they are chemically different. body. This work is done by the roots.be interesting to convey to the reader a We now see that it has besides to manufac- general idea of the nature of the agreement ture the materials-the gluten and fat-out and of the minute differences which prevail of which the soft parts of the animal are to between these and the other substances we be built up. This is done in the interior have classed along with them. of its root, stem, and leaves. We are indebted to Professor Mulder of Then as to the purposes of the several Utrecht for the observation, that if gluten, constituents of the food-the gluten is car- albumen, casein, fibrin, &c, be dissolved in ried into the stomach, and thence by the caustic potash, and an acid be then added proper vessel to build up almost unchanged to the solution, a white matter is separated, the muscular parts of the body. The which from every one of these substances fat also is merely transferred from the is the same-which exists in and forms stomach to the parts of the system where from 95 to 99 per cent. of them all—and to its presence is required, or where it is to which he has given the name of protein.† be laid up in store. The plant is thus the In fact, these substances are all compounds brickmaker and hodman, as it were, while of protein, with minute proportions of sulthe animal is the bricklayer, who selects phur and phosphorus, which in many cases the materials brought ready to his hand, have not hitherto been determined. It is dresses them a little, if necessary, with his upon these minute proportions of sulphur trowel, and fits them into their places. and phosphorus that the differences observed among these several substances as they exist in the animal and the vegetable in a considerable degree depend. The following table exhibits a simple view of the mutual relations of some of these compounds : Here, again, we see the beautiful adaptation of the plant to the animal-a distinct forethought, in obedience to which the plant prepares beforehand what the future animal is to require. The stomach of the animal is not fitted to manufacture the materials of its own body out of the raw elements which exist in the atmosphere and the soil. This labor, therefore, is imposed upon an inferior race of living things; but if this inferior race from any cause, cease to labor, the animal must cease to live. The life of man has been likened to a flower; but the humblest flower has, in reality, a more independent existence than he. This fundamental substance, protein, therefore, exists in a great number of those compounds of which the parts of our bodies consist. It is manufactured by the vegetable out of the elements or more elementary compounds of which it consists-exists, The analogy-the almost absolute identity-above shown to exist between the several parts of the plant and those of the animal, and the way in which the substance of * On his visit to the stud of the Pasha of Egypt, the one is directly converted into the substance of the other, shows how unfounded Colonel E. Napier says, "Amongst other things, I happened to mention the Indian system of fatis that prejudice which many entertain, that tening horses on chopped sheep's heads, and was a difference exists between animal and ve- not a little surprised when he said that he could getable food so essential, that the former is the more readily credit it, as to his person I knowwholly unfit to feed and support the herbivor-ledge the Arabs of the Hedjaz often feed their horses on dried flesh of the camel, as well as its ous races. The starch contained in vegetable milk, and that in some of the districts along the food does constitute an important distinc- coast, when barley was scarce, even dried fish tion between the two, and one which is con- was used for them as an article of food."-Wild nected, as we shall presently see, with very Sports in Africa, &c., ii., p. 206. beautiful and important purposes in the animal economy; but there are few animals, indeed, which may not be kept alive In chemical language, this protein is represented by C40, H3, N5, O12. Glutin is that part of the Gluten which is soluble in alcohol. therefore, in the vegetable food we eat and through the stomach is conveyed to the several parts of our bodies. In the stomach it may be altered, combined with more or less sulphur or phosphorus, but cannot be formed from its elements. Thus we see a little farther into the kind of duty which is imposed upon plants, and into the kind of dependence in which the animal is kept upon the labors of the vegetable kingdom. But even in the plant, while it is preparing for the animal, this protein serves important purposes. It is produced from the food of the plant in the first root that is formed. It is carried up and deposited along with the young wood. It is necessary in some way to the production of every cell. It is first laid down in the solid state along the walls of the young cells and ves sels-it chalks them out as it were. It is afterwards redissolved and shifted in the interior of the plant, probably to form new parts-old cells containing less of it, and young cells more-till at last it is allowed to accumulate in the seeds, from which man and other animals obtain it. Thus there is a unity of purpose and design throughout all the phenomena of life; and while on the way, as it were, to fulfil some great end, many minor purposes are served by every particle of living matter. and robs the land of this its special constituent. We are informed by Professor Johnston, in his Elements, p. 273, that the wool which is grown in Great Britain and Ireland carries off the land every year upwards of four millions of pounds of sulphur, to supply which would require the addition to the soil of 300,000 tons of gypsum. Things that appear trifling to us when viewed in the small way in which we actually see them, become important when considered on the large scale in which they take place in nature. The hair on the heads of our population carries off nearly half as much as the wool of our sheep it is not without reason, therefore, that the Chinese collect, and employ as a manure, the hair shaven every ten days from the heads of their people. We cannot advert to the numerous other practical deductions and applications which flow from what has been stated abovehow the kind of soil, the mode of culture, the condition of the land as to drainage, &c., modify the proportions of gluten, starch, and fatty matter in the crop-and how the proportion of these, again, in the food, determines, in a great degree, the rapidity with which, other things being equal, the animal we feed lays on muscle or fat. There are three substances in the above It is interesting, however, to observe, table, a moment's attention to which how still higher practical questions arise will give us an idea of the kind of changes out of such investigations. In feeding also which take place within the animal stock for the growth of beef or mutton, or body itself. These are the albumen of the in keeping dairy cows for the production blood, the fibrin, and the hair. It is one of milk and cheese, the husbandman is of the functions of the blood to repair and really a manufacturer. He raises certain rebuild the fibre of the muscles. Suppose raw materials in the form of grass, clover, the albumen of the blood to be changed and turnips, and he must convert them into into fibrin, it only loses one equivalent of beef and mutton, or into butter and cheese, sulphur. Thusbefore he can take them to market. the practical man, who has a rent to pay, the primary question is, In which of these ways can I turn my raw material to the best account? If the balance of profit, in his locality, is on the side of beef and mutton, he feeds cattle and sheep; if on the side of the milk, he makes butter and cheese. Protein. Sulphur. Phosphorus. 2 1 1 From one of albumen, 10 To But the country at large puts the question in another form. When the population is constantly ahead of the productive powers of the land, the primary question becomes, Such researches as the above are not" In which of these states-of beef or milk curious merely, or physiologically interest--can the largest quantity of human food ing; they have important bearings also on be manufactured from the same quantity of practical life. Thus the wool and hair to turnips, grass, or clover?" Professor Johnwhich we have just alluded, as containing ston has stated the amount of our present so much sulphur, necessarily draws upon | knowledge to be, that the same herbage will produce about five times as much human food ly diffused carbonic acid to form so large a in the form of milk as in the form of beef; proportion of its own substance. We are and adds-"Should the population of this also tempted to ask, why, if plants depend country ever become so dense as to render so much upon it, so small a quantity of this a rigorous economy of food a national ques- gas is diffused through the air? The answer tion, butcher meat, if the above data deserve and explanation of all, however, is simple. any reliance, will be almost banished from Animals live in this air as well as plants. our tables, and a milk diet will be the daily It must therefore be adapted to the nature sustenance of nearly all classes of society." of both. But if the carbonic acid had been Elements, p. 279. This result is very cu- present in much larger quantity, it would rious, and there is an unexpected interest have been injurious to animal life. To in finding chemical research thus connect- compensate, however, for this smallness of ing itself with the highest and most impor- quantity in adaptation to animal life, the tant considerations of our national economy. plant is made to shoot up a long stem, to thrust out long branches, and to suspend thousands of broad leaves in the midst of the ever-moving air, and thus, by millions of mouths at once, to drink in the minute particles of aerial sustenance, which together are to build up the substance of its growing parts. Thus the balance is kept up, while wisdom and beauty and prevision appear in the way in which it is effected. There remains one other important topic to which it is necessary to advert, in order, in some measure, to complete our sketch of the relations of chemistry to rural economy. We have already seen that the organic part of the plant contains much starch or sugar, while that of the animal contains none. What is the reason of this difference? We eat starch and sugar in our food, and yet they form no part of our bodies. They are not, like the gluten and the fat, built into our substance. What becomes of them, therefore? What purpose do they serve in the animal economy? Why do they exist so largely in all vegetable substances? These inquiries lead us to the discovery of other beautiful contrivances and other wise ends. The carbon thus drawn from the air unites with the water in the interior of the leaf or stem, and is changed into starch, or sugar, or woody fibre, all of which, as we have already seen, consists of carbon and water only. In this way, the starch we eat in our food is formed out of carbonic acid, drawn from the air by the leaves, and of water drawn from the soil by the roots. But what becomes of the starch after it has been eaten? What purpose does it serve in the an Plants draw their organic food-that food from which their organic part is formed-imal economy? in part from the soil, and in part from the air. Of that which they draw from the air, the carbonic acid is the most important. This carbonic acid consists of carbon (pure charcoal) and oxygen only. It exists in the atmosphere in exceedingly small quantity, five thousand gallons of air containing only two gallons of this gas. During the day, all the green parts of our cultivated plants are continually sucking in this gas from the air, and giving off oxygen, adding, in fact, to the proportion of carbon they contain. We are surprised at first to learn that upwards of three-fourths of the bulk of vast forests, as well as of the crops we reap from our fields, are in this way drawn from the air. We are astonished that the growing plant should be able, by all its diligence in working, to draw in enough of this sparing Carbonic acid is the kind of air which escapes from soda water, ginger beer, or champagne, and causes them to effervesce. Among the necessary functions of animal life is that of breathing. We breathe that we may live. During respiration, we draw into our lungs atmospheric air, containing, as we have seen, a very minute proportion of carbonic acid gas. But when we return the air to the atmosphere from our lungs, it contains a much larger proportion of this gas. It is constantly produced in the blood, and given off from the surface of the lungs into the air. A full grown man throws off as much carbonic acid every day as contains eight or ten ounces of carbon; a cow or a horse about five times as much. This carbon the animal derives in great part from the starch or sugar which it eats, and thus the purpose or function of all the parts of the food is explained. The gluten repairs the waste of the muscles, the oil lays on fat, the saline matters yield their necessary ingredients to the bones and the blood, and the starch feeds the respiration. The carbonic acid, it thus appears, is sucked out of the air by the plant, and its carbon combined with water into the new form of starch. The animal eats this starch, and after a while throws the carbon off again into the air in its old form of carbonic acid, ready to be taken up a second time by other plants, and to be reconverted into starch. This is no doubt a very beautiful little cycle of operations, by which a comparatively small quantity of carbon is made to perform a large amount of work; but if it be true to nature, the carbon must serve some useful purpose, while it is undergoing these successive transformations. The alternate production of starch and carbonic acid must have some connection with the well being of vegetable and animal existences. We shall for the present, pass over its use to the plant, and consider only the purpose it serves in reference to animal life. When starch or sugar is kindled in the air, it burns; its carbon combines with the oxygen of the atmosphere, and forms carbonic acid. Much heat is given off, and the starch entirely disappears in the form of carbonic acid and water. A similar change takes place in the body of the animal. The starch which is conveyed into the stomach is burned indirectly, by means of the oxygen which is taken in by the lungs. Heat is thus produced, while carbonic acid and watery vapors are given off in the breath. by which the other motions of the machine are kept alive. Nor are these explanations simple and beautiful only. The practical man learns from them that his stock ought to have a certain quantity of starch in their food, but that they can by no means live on starch alone. We say ought, because economy prescribes it. Animals will live-herbivorous animals that is-though there be no starch or sugar in their food. Fat may supply its place, or even beef and gluten in certain circumstances. But in our climate these are neither suited to the habits of our stock, nor are they economical to the feeder. The use of beef or gluten, indeed, in the place of starch, involves an absolute loss of most valuable nourishment. But the animal dies. The body is consigned to the dust. Its organic and inorganic parts there undergo numerous chemical changes, all of which are intended to adapt the dead matter for entering into the walls of new superstructures. To follow these changes would show us further beautiful contrivances and happy adjustmentsconnected also with reflections as high, with practical results as important, and with practical suggestions as useful as any of those we have already considered. We must, however, hold our pen; we have given instances enough to show how In our atmosphere, all sensibly warm sub-rich in instruction this whole subject isstances have a tendency to become cooler. how full of instruction especially to the The bodies of warm-blooded animals are improving agriculturist. How importhus constantly losing heat. Were there tant, therefore, in the present state of our no source of heat within the living body it- national agriculture, that these enlarged self, therefore, it would soon become cold means of good which the Deity offers us, and stiff as those of dead animals so quick- should be placed within the reach of our ly do. The burning of the food in the sys- practical men, and that these men should tem-for so it may be called-is this source be induced to employ them with a view to of heat; hence the coldness and the shiver- their individual as well as to the general ing of the half-fed, and the cheerful warmth welfare. of those who live well; hence also the larger consumption of food where much exercise is taken and much warmth expended, and the smaller appetite of those whose lives are sedentary, or who live in comfortable houses. Had our limits permitted us, we could have wished now to advert to the origin and progress of this knowledge,―to have inquired how, when, and by whom these applications of science to agriculture have been successively made. We should have liked to explain how Lord Dundonald first drew together the scattered fragments of such knowledge in our own country-how Davy built upon and added much to this foundation-how De Saussure, meanwhile, was enlarging by important facts and deductions our knowledge of the chemical physiology of plants-how, following in the footsteps of these men, Sprengel almost alone during a lapse of twenty years, grad |