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same year he completed his Suburban Horticulturist; and finally, in 1843, he published his work on Cemeteries, the last separate work he ever wrote. In this list, many minor productions of Mr. Loudon's pen have necessarily been omitted; but it may be mentioned, that he contributed to the Encyclopædia Britannica and Brande’s Dictionary of Science; and that he published numerous supplements, from time to time, to his various works.

No man, perhaps, has ever written so much, under such adverse circumstances, as Mr. Loudon. Many years ago, when he came first to England (in 1803), he had a severe attack of inflammatory rheumatism, which disabled him for two years, and ended in an anchylosed knee and a contracted left arm. In the year 1820, whilst compiling the Encyclopedia of Gardening, he had another severe attack of rheumatism; and the following year, being recommended to go to Brighton to get shampooed in Mahommed's Baths, his right arm was there broken near the shoulder, and it never properly united. Notwithstanding this, he continued to write with his right hand till 1825, when the arm was broken a second time, and he was then obliged to have it amputated; but not before a general breaking up of the frame had commenced, and the thumb and two fingers of the left hand had been rendered useless. He afterwards suffered frequently from ill health, till his constitution was finally undermined by the anxiety attending on that most costly and laborious of all his works, the Arboretum Britannicum, which has unfortunately not yet paid itself. He died at last of disease of the lungs, after suffering severely about three months; and he retained all the clearness and energy of his mind to the last.

His labours as a landscape-gardener are too numerous to be detailed here, but that which he always considered as the most important, was the laying out of the Arboretum so nobly presented by Joseph Strutt, Esq., to the town of Derby.

Never, perhaps, did any man possess more energy and determination than Mr. Loudon; whatever he began he pursued with enthusiasm, and carried out, notwithstanding obstacles that would have discouraged any ordinary person. He was a warm friend, and most kind and affectionate in all his relations of son, husband, father, and brother; and he never hesitated to sacrifice pecuniary considerations to what he considered his duty. That he was always most anxious to promote the welfare of gardeners, the volumes of this Magazine bear ample witness; and he laboured not only to improve their professional knowledge, and to increase their temporal comforts, but to raise their moral and intellectual character.

Art. II. Comparative Physiology. By R. LYMBURN.

(Continued from p. 578.)

In Chap. VIII. On Nutrition and Formation of Tissues, General Considerations, it is remarked : -“ The nature of the absorption of the alimentary fluid, and the means of transmitting it to the distant parts of the system, having now been considered, the question next arises, how the nutritive ingredients thus introduced are applied to the developement and maintenance of the several portions of the structure. The conversion of the inorganic elements of the food of vegetables into complex tissues so entirely different from their components, is a process in which several stages may be traced with considerable distinctness; and although the food of animals is not so simple, yet the alterations which it undergoes in composition and properties are scarcely inferior in extent or peculiarity of character. The imperfection of our present means of observation has caused great ignorance of the nature of these changes. The recent application of polarised light to the examination of vegetable juices has shown important differences in nutritious principles, not before suspected. Where, as in the higher plants and animals, the alimentary materials are not so speedily organised as in the lower, the complex nature of the process requires considerable alteration in the character of the nutritious fuid, before being applied to its ultimate purpose, the food being prepared into substances ready to be assimilated by the various tissues : probably, also, the lower beings go through similar unperceived changes with their food, as solid structures cannot assimilate matter without being first formed into combinations differing essentially from the inorganic. The blood of animals contains

various ingredients

, produced subsequently to the reception of the food into the stomach, prepared for the reparation and maintenance of the several tissues; and the elaborated sap of vegetables contains other principles peculiar to its structure, and adapted to its maintenance: these are called organisable products, the proximate principles of chemists being made to contain, besides these, many of the peculiar secretions and excretions, as they are stored up or excreted, and not the materials only. Of the manner in which the organisable products are formed from their elements, little is positively known; but late chemical researches favour the opinion that their elements are held together by affinities that do not differ from those which operate in the productions and changes of the combinations presented to us in the inorganic world; and that, being subject to the same laws, they may be made to exhibit analogous phenomena. The conversion of organisable products into organised tissues is a process entirely different from the production of the former, and takes place under the laws of vitality alone. The power of communicating to nutritious matter their own structure and properties, which is characteristic of living beings, is also peculiar to each of their component textures. From the same circulating fluid, of uniform character in every part of the body, is developed in one spot muscular fibre, in another nervous tissue, in another solid osseous matter, and so on; the new matter being deposited in continuity with the previously existing structure. The circulating fluid is also possessed of properties that must be considered vital, since they differ from any which a mere mechanical admixture of the ingredients could present. The aliment absorbed, while still fluid, is endowed with qualities which prepare it for its final assimilation. In tracing the alterations which occur from absorption to assimilation, it will be desirable to examine them just as they occur in the higher classes of plants and animals, and then apply the results thus obtained to the more simple.'

The preparation of the elaborated sap in the leaf has been compared to that of digestion, but is entirely different in character. The action in the leaf requires the highest chemical powers to be exerted. The decomposition of carbonic acid, water, and ammonia into their elements, and combining of them again into the organisable products fit to serve for nutrition to the vegetable organs, cannot be compared to the preparation of the animal food in the stomach, which is one of solution merely, not combination, and similar to that of the solution of the vegetable food in the soil, the stomach of the plant. Liebig says:

" Those vegetable principles, which in animals are used to form blood, contain the chief constituents of blood, fibrine and albumen, ready formed, as far as regards their composition. All plants, besides, contain a certain quantity of iron, which reappears in the colouring matter of the blood. Vegetable fibrine and animal fibrine, vegetable albumen and animal albumen, hardly differ, even in form. Vegetables produce in their organism the blood of all animals; for the carnivora, in consuming the blood and flesh of the graminivora, consume, strictly speaking, only the vegetable principles which have served for the nutrition of the latter. Vegetable fibrine and albumen take the same form in the stomach of the graminivorous animal, as animal fibrine and albumen do in that of the carnivorous animal.

In this sense we may say the animal organism gives to blood only its form ; it can form other compounds, differing in composition from the chief constituents of blood; but the above, which form the starting point of the series, it cannot produce. The fat of beef and mutton occurs in cocoa beans, human fat in olive oil, the principal ingredient of butter in palm oil, and horse fat and train oil in certain oily seeds. From the caseine of the mother's milk of animals, which is identical with fibrine and albumen, and with the caseine of beans, peas, and lentils, are produced the muscular fibre, cellular tissue, nervous matter, and bones of the young animal. These three, fibrine, albumen, and caseine, have all for their basis the substance discovered by Mulder, called proteine, and differ only in the quantity of sulphur, phosphorus, and inorganic matter they contain. Vegetables produce in their organism compounds of proteine, out of which the various tissues and parts of the animal body are developed by the vital force, with the aid of the oxygen of the atmosphere, and the elements of water.”

He afterwards describes digestion as a chemical transformation only, similar to that of putrefaction and fermentation, but without disengagement of gas, which takes place in many other cases besides digestion. The gastric juice he considers a principle formed from the decomposition of the membrane of the stomach itself, which, like diastase, yeast, and other substances in decay, have a tendency to communicate and promote decay in others. This principle, with the help of the oxygen and water of the saliva, dissolves the substances introduced ; the muriatic acid poured out from the stomach along with the gastric juice, on the stimulus of food, checks the dissolution from proceeding farther to the state of fermentation or putrefaction. Besides the muriatic acid, iron, he says, is also found in the gastric juice, which, he thinks, assists in the oxidation of the waste in the blood, by being formed into peroxide by the absorption of oxygen in the lungs by the globules which contain the iron, and returning to the state of protoxide by giving off its oxygen in the capillaries or veins. Lactic acid has been said by others to assist in these processes, but erroneously he thinks, as it is not a normal production of the body, never being found formed unless accidentally, which is exceedingly apt to take place. The muriatic acid is formed from salt, so necessary to all animals in their food, and will dissolve bones as well as lactic acid; the soda is used in the formation of bile, &c. The longer digestion continues, he says, and the greater the resistance offered to the solvent action by the food,

the more the saliva and the air it contains

* All substances in action, he says, have their molecules in an active state, and this action they communicate to similar substances they come in contact with. The activity of the molecules of organised substances, when in a state of forming vital products, communicates that state, or vitalises organisable and organised substances when they come in contact with them. In the same way, if in a state of decomposition, as yeast, diastase, and gastric juice, they communicate that state of decomposition, which will go on, he says, as long as nitrogen is furnished, unless counteracted by some other substance.

enter the stomach, which is partly the benefit of rumination. The nitrogen set free is, he thinks, given out by the skin and lungs; some have denied this, but it seems generally admitted that animals assimilate no free nitrogen. Guided probably by this, however, Liebig has denied to plants the power of assimilating free nitrogen, which is contended for by Boussingault and others, and without which the quantities of nitrogen drawn off by some plants without impoverishing the soil cannot be accounted for. Plants have a much greater chemical power of forming organisable products from their elements; and, if nitrogen is introduced by the roots or leaves, and, in its nascent state especially, when newly separated from oxygen, is in contact with hydrogen from decomposed water, it is as likely to form ammonia then, as in the processes of combustion and oxidation, which are chief sources of ammonia.

The great chemical power exerted by plants in the leaves, to which the assistance of light is essential, seems to be totally different from any thing to be found in animals, in whom there is no power of forming organisable products from their elements, as in plants. The above extracts, from the comprehensive and condensed work of Liebig, seem to characterise that of digestion in animals as similar to that of solution in the soil. Plants differ from animals in being preparers of organised products by forming them from their elements, which animals are wholly unable to do; and this function of separating the substances imbibed into their elements, and again recombining them into organisable products or proximate principles (which, in Brande’s Dictionary of Science, newly published, appear to be taken as synonymous), should have some epithet distinctive of its peculiar nature attached to it, and not be confounded with that of digestion, which it does not at all resemble.

It is still uncertain, however, whether it may ever be in the power of chemists to demonstrate that the elements of these organisable products are held together by the same affinities, subject to the same laws, and may yet be made to exhibit analogous phenomena. Professor Thomson and other chemists seem too sanguine in the same opinions as those above noticed of Dr. Carpenter. Professor Johnson, in his valuable Lectures on Agricultural Chemistry, gives a very detailed view of the subject, and seems to be very dubious of any such result being ever arrived at. Schlieden, and physiologists in general, say tion is principally organic. Chemists have been able to transpose lignine, starch, sugar, and gum into each other, chiefly in the descending series, principally by the aid of heat and sulphuric acid.

In the ascending series, lignine has been formed by nitric acid

the ac

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