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from which they are produced, while the more fluid matter in which they are dissolved contains the salts of the blood, and often its alkali in the same proportion as the blood itself. Professor B. observes, that those secretions, which before their discharge are intended to be applied to some purpose within the body, are always alkaline, while those which are to be carried off as useless to the animal, are all acid, the free acid they contain being the lactic.
Our author now proceeds to notice the cellular texture, and the fluids connected with it. He considers the gelatine obtained by boiling the cellular texture in water, as a product formed during the process, and not as one of its constituent parts; observing that no precipitate resembling that produced by tannin and gelatine, can be obtained from any animal fluid, except from urine after having been boiled sometime with alkali, by which means its animal matter is either entirely or in part converted into gelatine. In adverting to the fat which is found deposited in the cells of the cellular membrane, he remarks that the acid obtained by.the distillation of fat, and which has been described by Crell, 'Thenard, and others as a peculiar acid under the name of sebacic, is, in fact, possessed of all the properties of benzoic acid, except in a few of its external characters, which he apprehends result from the combination of some other products of the distillation, by which both its taste and smell are modified. In detailing what has been done to determine the nature of pus, he observes, that the modes of examination suggested with a view to a correct discrimination of pus from mucus have failed, from the want of correct notions on the subject. The Professor very properly considers as pus, not only the fluid produced by inflammation terminating in an abcess, but also the yellow matter (expectorated after inflammation in the lungs, for example,) formed in the decline of inflammatory action, and without any distinction of parts; both fluids being produced from the coloured blood, which, during inflammation, is propelled into the capillary vessels. As, however, that which is produced in the cellular texture, can only escape by the destruction of the neighbouring parts, he thinks it would be found on a comparative examination to contain more constituent parts, than that which is formed on the surface, and is mixed only with mucus. The investigations of Dr. Pearson on this subject are mentioned with approbation, though our author thinks he had not sufficient experience in these inquiries, to make them altogether satisfactory. Dr. P.'s animal oxyd affords an instance of this, which the Professor states to be merely the viscid extract, obtained in the analysis of most animal substances, and consisting of muriate of soda, alkaline lactate, and some peculiar animal matters. Vol. X.
The next object of the Professor's notice, is the mucous membrane which lines the intestinal canal, and all the reservoirs of the body, with their excretory ducts. The principal characteristic of this membrane is its insolubility in boiling water : it is not, like cellular texture, and serous membrane, converted into gelatine by boiling; and, with the exception of the brain, it is of all parts of the body most easily destroyed by maceration in cold water, or by the action of acids. The mucus with which it is covered, though varying but little in its external characters, yet differs considerably in its chemical properties, according to the nature of the substances with which it is to come in contact. Mucus in its chemical composition is not a solution : it contains a solid matter, which swells in water, and becomes a tough semi-liquid mass, which water does not dissolve. The more fluid portion of mucus is serum, almost deprived, indeed, of its albumen, yet retaining its other constituent parts. Professor B. does not admit the existence of an animal mucus in the fluids of the animal body, distinct from that which covers the mucous membranes. In all his experiments he never found any fluid to which the name could properly be applied, or which agreed in character with mucus as described by Hatchett, Bostock, and others. Fourcroy, also, in his paper on mucus, he observes, has fallen into the error of drawing general and extensive conclusions from very uncertain, and oftentimes incorrect observations; and he has generalized so far as to consider parts of the body having very different chemical and physiological characters, (such as the epidermis, nails, hair, &c.) as nothing but mucus, more or less condensed and hardened. The mucous membrane of the intestinal canal is the only one having a specific character; its dense cellular texture, and muscular coat, having the same chemical character as the same structures in other parts of the body: and the serous membrane or peritoneal covering, as it is commonly called, which envelopes the whole, is fundamentally the same as the cellular texture. The serous fluid with which this membrane is constantly moistened, is chiefly serum, containing only a small portion of its albumen, and depositing chrystals of muriate of soda, and the usual viscid animal extract, during evaporation.
Of the fluids employed, more or less, in the digestive process, the saliva comes first to be noticed. Professor B. observes, that it is one of the most aqueous fluids in the body. The white mucous matter suspended in it, he thinks is most probably derived from the mucous membrane of the salivary ducts; but besides this, and the usual salts contained in the serum, it has a peculiar matter which is not coagulated either by boiling, by tannin, or by the subacetate of lead, and which with water forms a liquid frothy solution. How far saliva may contribute to the solution of the food, is yet unknown to us. From the mucus diffused through the saliva, the tartar which adheres to the teeth is formed. It consists at first merely of darkened mucus, but phosphat of lime is slowly deposited, and the crust which is gradually formed, contains about its weight of mucus.
The facts with which we are supplied by former experimentalists on the nature of the gastric juice are extremely limited: nor does Professor B. make us acquainted with any new ones relatively either to it, or the pancreatic secretion. His examination of the bile, however, has enabled him to correct and extend our knowledge of this important secretion. Notwithstanding the reports of other chemists, he found that it does not contain any resin ; that it has the same proportion of alkali and salts as the blood; and that it contains a peculiar matter, which is at first bitter, and afterwards rather sweet to the taste, which possesses characters in common with the fibrin, the colouring matter, and the albumen of the blood, and which forms, with mineral acids, a compound not easily soluble in water. With excess of acid this substance is completely precipitated, and has all the characters of a resin, but the separation of the acid, by a body having a superior affinity (barita for example) restores its original properties unchanged. Like the albumen and fibrin of the blood, it is not precipitated by acetic acid. Its properties vary in different animals, and even in thesame animals in different circumstances; and the Professor had opportunities of observing, that its remaining long in the gall bladder, increased its tendency to form a resinous compound in the acids. The substance which has by other experimentalists been considered as albumen, and to enter into the bile as one of its constituent parts, our author thinks he has demonstrated to be merely a portion of the mucus of the gall bladder. The proportion of it is very sinall, and thick viscid bile does not appear to contain more of it than that which is quite thin.
The account of the process of digestion which follows this account of the chemical properties of the fluids concerned in it, is almost purely historical; and supplies a neat and condensed view of the labours of others, in this important department of physiological enquiry. Our author does not appear to have much faith in the recent speculation of Sir Everard Home relative to the division of the stomach into two portions, by a contraction of its muscular fibres, during the time the digestive process is going forwards: and certainly, the anatomical structure of the stomach is very unfavourable to the hypothesis. The composition of the chyle, for the formation of which the complicated process of digestion is carried on, appears, from all observations, to resemble the blood in every thing but its colour, except that it is much more dilute; but upon what circumstances its change of colour depends after it is mixed with the blood, is very obscure—though it is probably effected, in great measure, by the atmespheric air to which it is exposed in the lungs.
In proceeding to consider the composition of the bony part of the animal structure, Dr. B. manifests a pardonable anxiety in asserting the claims of his countryman Gahn, to the honour of having first discovered the existence of the phosphat of lime in bones, from which they drive their firmness and solidity. In addition to this, however, the Professor informs us, that he has discovered, by a careful and minute analysis, that a human bone contains also fuat of Ime and phosphat of magnesia; and he has satisfied himself that the sulphat of lime, which is found in the residuum after combustion, does not belong to bone in its living state He estimates the proportion of cartilage at }, but it is less in the teeth, and in the enamel it is altogether wanting. The combustible matter in the enamel, he estimates at only 2 per cent, while Pepys states it at 16, and Fourcroy and Vauquelin at 27. The bone of the ox contains the same constituents, and nearly in the same proportion as that of man. The cartilage of bones is converted into gelatine by boiling, and it may be extracted in this form almost entirely by the use of Papin's digester. The marrow Professor B. considers as precisely similar to the fat in other parts of the body, any apparent difference being attributable to the fluids proper to the membrane in which it is enclosed. The cartilage, properly so called, is exactly the same with that which enters into the composition of bone, and, like it, is converted into gelatine by boiling in water. The sinovia appears to be almost entirely serum, but still retaining a portion of fibrin which coagulates in the open air.
. In his experiments to determine the nature of the muscular part of animals, the Professor found that it included about its weight of a fluid containing a free acid, and affording the usual viscid extract consisting of lactic acid, alcaline lactate, muriate of soda and animal matter. This extract, however, he does not consider as a constituent part of flesh, but rather as matter in a state of decay, either already absorbed, or ready to be taken up by the absorbents for the purpose of being removed from the system. The solid muscular fibre itself has the same properties as fibrin; the whole of it being soluble in acetic acid, except the cellular texture, nerves and blood vessels, and undergoing the same changes - by boiling. The tendons and aponeuroses have fundamentally the same composition as the cellular texture and cartilage. The sclerotica, choroidea, and corner of the eye are all converted into gelatine by boiling water; but the black colouring matter spread over the inner surface of the choroid, is insoluble in water at any temperature, and in acids; but caustic alkali dissolves it, and it is precipitated by acids, the colour being rendered somewhat paler. It burns like vegetable matter, and leaves the same ferrugineous ashes, as the colouring matter of the blood, from which it is most probably formed. The iris has all the chemical characters of muscle. Of the humours of the eye, the aqueous and vitreous resemble the fluid secreted by mucous membranes, only they are quite colourless; the chrystalline lens, however, is as remarkable in its composition as in its texture, which is well known to increase in density from the circumference to the centre. It has been assertetl, both by Fourcroy and Chenevix to contain both albumen and gelatine, but Professor B. in his examination of it, found neither of these substances. It is almost completely soluble in water, and the solution coagulates on boiling, but the coagulated mass has no resemblance to albumen ; it is gritty and opaque like the colouring matter of the blood, and like it is also easily dissolved in acetic acid after coagulation. The coagulation is a pure white, and leaves a small quantity of ferrugineous ashes after combustion, so that it seems to differ from the colouring matter of the blood, only by its want of colour, but the attempts to impart colour to it, by different modifications of the phosphat of iron have been unsuccessful. Less aqueous than the blood, it
appears to form the boundary between the fluids and the solid matter of the animal body. When analysed, it affords a portion of acidulous extract. Its structure, therefore, cannot be considered in any degree muscular. The texture of the epidermis is peculiar, since it is not dissolved by long boiling in water, but is soluble both in the caustic alkalies and acids; in most of its chemical characters it resembles the hair and the nails. The experiments on the matter of transpiration though very numerous, have been more directed to ascertain its quantity, than its chemical composition; it is known, however, to be always acid ; and Professor B. found it to contain muriate of soda, and to exhibit marks of the usual viscid extract, as well as of matters insoluble after spontaneous évaporation, and which had the, smell of albumen when burnt. The nails appear to be composed of the same matter as the epidermis.
Scarcely any portion of animal inatter has been more frequently the subject of chemical examination than the urine, and for reasons sufficiently obvious; since a knowledge of its nature might be expected to throw some light upon one of the most painful of human maladies. After a brief and very candid notice of what has been accomplished by others, the Professor proceeds to state what has been done by himself on this subject. He has ascertained that the free acid in urine, is not as has been supposed by others, either the acetic or phosphoric acids, but consists of the lactic and uric acids. In the phosphat of lime,