1847]

Composition of the Juices of Flesh.

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may be extracted from muscle, the author next describes Lactic Acid as forming one of the constituents of flesh, and passes on to the consideration of the Inorganic Constituents of the Juices of Flesh, which he treats of at very considerable length. Into his ingenious speculations upon the important agency of the saline constituents, the alkaline phosphates, of the juice of flesh, and upon the function of the phosphate of soda in the blood -that of absorbing carbonic acid and giving it out in the lungs-our limits forbid our following him. An extract or two will exhibit the interesting character of the subjects adverted to. After stating that Lactic Acid cannot be detected in the urine even of those to whom it has been administered, he goes on to observe.

"From this it plainly appears, that the lactic acid in the organism is employed to support the respiratory process, and the function performed by sugar, starch, and in general all those substances which, in contact with animal matter are convertible into lactic acid, ceases to be an hypothesis. These substances are converted in the blood into lactates, which are destroyed as fast as they are produced, and which only accumulate where the supply of oxygen is less, or where some other attraction is opposed to the agency of that element. When we consider that the urine of graminivorous animals contains a large quantity of free alkali, which is secreted from the blood; that, consequently, in the blood a current of dissolved alkalies is carried through the whole mass of the body, and especially through the substance of the muscles, while the fluid which is in contact with the external part of the blood-vessels and lymphatics (the juice of flesh) retains an acid reaction, we perceive that a cause must necessarily be in action at these points, which prevents the removal of the free acids, or, if they are removed, reproduces them at each moment of time.

"The blood-vessels and lymphatics contain an alkaline fluid, while the sur rounding fluid, that of the flesh, is acid; the tissue of which the vessels are composed is permeable for the one or the other of these fluids. Here then are two conditions favorable to the production of an electrical current, and it is far from improbable, that such a current takes a certain share in the vital processes, although its action be not always indicated by proper electrical effects." P. 104. "From the great difference of chemical nature and qualities in the fluids circulating in the different parts of the organism, it follows, that there must be a very remarkable difference in the permeability of the parietes of the vessels for these fluids. Were this permeability in all cases the same, there must have been found as much of the salts of soda and potash in the juice of flesh as in the blood; but the blood of the ox and the fowl contains nearly a third of its whole saline contents of chloride of sodium, while hardly a trace of this compound occurs in the juice of flesh.

"The vessels which secrete milk must stand in a similar relation to the bloodvessels; for in the milk of the cow, the salts of potash preponderate very greatly over those of soda, and are present also in much larger quantity than in the saline constituents of blood.

"In some pathological conditions there has been observed, at points where bones and muscles meet, an accumulation of free lactic and phosphoric acids, which has never been perceived at those points in the normal state. The solution and removal of the phosphate of lime, and therefore the disappearance of the bones, is a consequence of this state. It is not improbable that the cause, or one of the causes, of this separation of acid from the substance of the muscle, is this that the vessels, which contain the fluid of the muscles, have undergone a change, whereby they lose the property of retaining within them the acid fluid they contain.

The constant occurrence of chloride of sodium and phosphate of soda in the

blood, and that of phosphate of potash and chloride of potassium in the juice of flesh, justifies the assumption that both facts are altogether indispensable for the processes carried on in the blood and in the fluid of the muscles.

Proceeding on this assumption, the necessity for adding common salt to the food of many animals is easily explained, as well as the share which that salt takes in the formation of blood, and in the respiratory process." P. 109.

Practical Applications.-In this section Professor Liebig furnishes some useful hints upon the modes in which animal substances can be most advantageously prepared for human sustenance. From raw flesh intended to reproduce itself in the animal frame, none of its constituents should be withdrawn during the progress of cooking. "The water in which flesh has been boiled contains soluble alkaline phosphates, lactates, and isoninates, phosphate of magnesia, and only traces of phosphate of lime; the boiled flesh contains chiefly, with the fibrine, &c., the insoluble inorganic constituents, phosphate of lime and phosphate of magnesia." If therefore, the flesh be eaten without the broth it becomes the less adapted for nutrition, and that in proportion to the quantity of water employed, and the duration of the boiling. "It is clear that all the sapid and odorous constituents of flesh exist in the flesh itself in the soluble state, and consequently when it is boiled are transferred to the soup. The smell and taste of roasted flesh arise from the soluble constituents of the juice, which have undergone a slight change under the influence of the higher temperature. Flesh, which has been rendered quite tasteless by boiling with water, acquires the taste and all the peculiarities of roasted flesh, when it is moistened and warmed with a cold aqueous infusion of raw flesh, which has been evaporated until it has acquired a dark brown colour." It is upon those soluble constituents the peculiar flavour of each kind of flesh depends, so that if to boiled beef a concentrated cold aqueous infusion of vension or fowl be added, and the mass warmed, the beef can no longer be distinguished from venison or fowl. "A slight addition of lactic acid (a very little sauer kraut, for example), or of chloride of potassium, which is an invariable constituent of all infusions of flesh, heightens the piquancy of the flavour of meat; as, on the other hand, an alkaline liquid, or the addition of blood, renders the soup of meat utterly insipid and mawkish." By the agency of cold water, also, all the albumen which every where surrounds the muscular fibre in a liquid form may be obtained; the quantity obtainable bearing an inverse ratio to the age of the animal. Old animals are, however, richest in fibrine, which, when deprived of its albumen becomes hard and horny in proportion as it is boiled. The tenderness of cooked meat, therefore, depends upon the amount of albumen coagulating between the fibres, and thus preventing the hardening of these. The duration of the boiling is another point to be attended to; for when this is too prolonged the albumen becomes harder, though not tough.

The following are the directions given for the best method of boiling meat.

"If the flesh intended to be eaten be introduced into the boiler when the water is in a state of brisk ebullition, and if the boiling be kept up for some minutes then so much cold water added as to reduce the temperature of the water to 165° or 158°, and the whole kept at this temperature for some hours, all the conditions are united, which give to the flesh the quality best adapted to its use as food.

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Rationale of Cooking Processes.

411

"When it is introduced into the boiling water, the albumen immediately coagulates from the surface inwards, and in this state forms a crust or shell, which no longer permits the external water to penetrate into the interior of the mass of flesh. But the temperature is gradually transmitted to the interior, and there effects the conversion of the raw flesh into the state of boiled or roasted meat. The flesh retains its juiciness, and is quite as agreeable to the taste as it can be made by roasting; for the chief part of the sapid constituents of the mass is retained under these circumstances, in the flesh.

"If we reflect that the albumen of the juice of flesh begins to coagulate at a temperature of 105.5° and that it is completely coagulated at 140° (Berzelius), it might be supposed that it would not be necessary, in the cooking of flesh, to expose it to a higher temperature than 1409. But, at that temperature, the colouring matter of the blood is not yet coagulated; the flesh, indeed, is eatable, but when it contains blood, it acquires, under these circumstances, a bloody appearance, which it only loses, when it has acquired, throughout the whole mass, a temperature of 150° to 158°.

"The introduction of the piece of raw flesh into water already boiling is the best process for the dressing of the meat, but the most unfavourable for the quality of the soup. If, on the contrary, the piece of raw meat be placed in cold water, and this brought very gradually to the boiling point, there occurs, from the first moment, an interchange between the juices of the flesh and the external water. The soluble and sapid constituents of the flesh are dissolved in the water, and the water penetrates into the interior of the mass, which it extracts more or less completely. The flesh loses, while the soup gains in sapid matters; and, by the separation of albumen, which is commonly removed by skimming, as it rises to the surface of the water when coagulated, the surface of the meat more particularly loses its tenderness and shortness (as it is called), becoming tough and hard. The thinner the piece of flesh, the more completely does it acquire the last-mentioned qualities; and if in this state it be eaten without the soup, it not only loses much of its nutritive properties, but also of its digestibility, inasmuch as the juice of the flesh itself, the constituents of which are now found in the soup, are thus prevented from taking part in the digestive process in the stomach. The soup, in fact, contains two of the chief constituents of the gastric juice." P. 128.

It has long been supposed that the chief properties of soup depended upon the amount of gelatinous matter dissolved during boiling; but, in fact, gelatine is tasteless and exists in a very small quantity in properly prepared soup. The nutritious and sapid ingredients exist ready formed in the flesh, and are in no-wise the products of the boiling. They may be most promptly extracted by following this formula for the preparation of soup :

"When 1 lb. of lean beef, free of fat, and separated from the bones, in the finely-chopped state in which it is used for beef-sausages or mince-meat, is uniformly mixed with its own weight of cold water, slowly heated to boiling, and the liquid, after boiling briskly for a minute or two, is strained through a towel from the coagulated albumen and the fibrine, now become hard and horny, we obtain an equal weight of the most aromatic soup, of such strength as cannot be obtained, even by boiling for hours, from a piece of flesh. When mixed with salt and the other usual additions by which soup is usually seasoned, and tinged somewhat darker by means of roasted onions or burnt sugar, it forms the very best soup which can in any way be prepared from 1 lb. of flesh." P. 132.

By concentration and slow evaporation a valuable extract of flesh may

be prepared, half-an-ounce of which converts 1 lb. of water into a strong well-flavoured soup. This portable soup (a very different one from that ordinarily so called which consists of gelatine), although too dear to form an article of commerce, is well worthy the attention of governments, as a restorative for wounded soldiers, and in the provisioning of ships and fortresses, as a means of preventing or relieving disease arising from a dearth of fresh meat and vegetables.

The effects of salting meat have been carefully investigated by Liebig, and he has ascertained that the brine in contact with the meat contains the constituents of a concentrated soup or infusion of meat; so that by this process the composition of meat becomes much more changed than by boiling. In the latter, "the highly nutritious albumen remains in the coagulated state in the mass of flesh, but, in salting, the albumen is separated from the flesh; for when the brine from salt meat is heated to boiling, a large quantity of albumen separates as a coagulum." It contains likewise, lactic acid, the phosphates, kreatine and kreatinine; and, in proportion as these are abstracted from the meat does it lose its nutritive properties. A portion of such flesh is converted into an element of respiration ; and health cannot be maintained upon salt meat, unless a much larger quantity be given, "inasmuch as it cannot perfectly replace, by the substances it contains, those parts of the body which have been expelled in consequence of the change of matter, nor can it preserve in its normal state the fluid distributed in every part of the body, namely, the juices of flesh."

We conclude our notice of Professor Liebig's interesting work with the following extract:—

"If we consider that the juice of flesh, in all animals yet examined, possesses a constant character; that, exclusive of those constituents which are derived from the blood unavoidably mixed with it, as well as of small quantities of odorous and sapid substances on which the characteristic secondary or by-taste of the juice or soup of the flesh in each kind of animal depends, the juice of ox-flesh is in no way distinguishable from that of the fox, it seems justifiable to conclude, that the quantity and the nature of the soluble constituents in the muscular system are essential to the functions of the muscles. It appears further to follow, that in judging of the nutritive qualities of any kind of food, the composition of the blood cannot be selected as the proper datum from which to argue, because there are a number of factors which must be brought into the calculation, and which are either wanting in the blood, or present in it only in trifling quantity.

"Some experiments have lately been made by Lehmann on the gastric juice of dogs, fed on bones and lean horse-flesh, which fluid he has studied more minutely than had previously been done. He obtained from it a crystallised salt of magnesia, combined with an organic acid, not containing nitrogen. This salt yielded 16.6 p. c. of magnesia, and 21 p. c. of water of crystallisation. Now that we know that lactic acid forms a constituent of the chief mass of the body, it is evident that Lehmann's magnesian salt, which agrees with lactate of magnesia in the proportion of base and of water of crystallisation, really was lactate of magnesia. In that case the gastric juice contains lactic acid, and thus the problem of the digestive process in the stomach would appear, in its chemical aspect, to be completely solved.

"The experiments of all who have studied the gastric juice agree in this, that that fluid contains, along with an organic acid, free phosphoric acid or an acid phosphate, and in this respect its similarity with the juice of the muscles is

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Chemico-Histology.

413

strikingly obvious. That portion of the gastric juice which is soluble in alcohol is, in its reaction, identical with the alcoholic extract of soup, as Tiedemann and Gmelin have already shown; and the soup or infusion of meat, free from gelatine and fat, the preparation of which I have described, may perhaps admit of being employed as a valuable remedy for many dyspeptic patients, with the view of increasing the activity of the stomach, and promoting digestion. Again, if the blood or the muscular substance of emaciated convalescents cannot supply the matters necessary for digestion in sufficient quantity for a rapid reproduction of the lost strength (that is, the lost parts of the organism), the benefit derived from well-made soup during convalescence admits of a simple explanation." P. 139.

Although forming but a single chapter in continuation of his work upon the "Chemistry of Vegetable and Animal Physiology," Professor Mulder, as Mr. Johnston remarks, has in fact produced a distinct treatise upon a novel subject-CHEMICO-HISTOLOGY. The anatomical doctrine of minute structures can only be investigated by the skilful use of the microscope. Their chemical nature, and the changes of composition which they undergo during progressive growth, or by the agency of disease, can only be determined by the joint use of the microscope and of varied chemical re-agents. The skill and dexterity of the ordinary histologist must be united to the knowledge and refined manipulations of the practised chemist, before any results can be obtained, which shall be of real service to vegetable and animal physiology." In this point of view the present work is not merely the best but the only one of the kind existing in which the student will find the histological and chemical characteristics of the various vegetable and animal tissues set forth with remarkable perspicuity and completeness, and illustrated by some excellent coloured engravings. Whatever may eventually be the fate of the author's views concerning proteine and its oxides, these researches and observations must ever remain a monument to his analytical skill and unwearied industry. The instructive details in which this work abounds must be referred to in the book itself, which will become an indispensable companion to every chemist and microscopist, who is desirous of acquiring a correct knowledge of structures hitherto imperfectly described or erroneously confounded with each other. One or two of the more general observations are all we can attempt to lay before our readers. Treating of the importance of considering the form, as well as the composition of parts, he observes :—

"The invaluable investigations, which of late years have been made with the microscope, have proved, that organs performing the same functions consist of the same kind of tissue; whilst those performing different functions consist of different tissues. This leads to the just conclusion, that the form of the parts of which an organ is built up, or by which a function is performed, is in close connection with that function itself, and that, on the other hand, the function is dependent upon the form. If the form be really dependent on matter and the forces residing therein, the function is dependent upon this also. In organic nature, therefore, matter, form, and function go together, and the one being different, the other will necessarily be different also.

"This view of the subject applies as well to all the sickly conditions of any organ, or of the whole organism, as it does to all the healthy functions of plants and animals. The connection existing between different organs of the animal body by nerves and vessels, and both of the animal and vegetable body by cells, is of such a kind, that Bichat's wish-that the organism might some day be

NEW SERIES, NO. XII.—VI.

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