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Part Third.

EXCERPTA.

1.-On the Mutual Relations existing between Physiology and Pathology, Chemistry and Physics, and the Methods of Research pursued in these sciences. By BARON LIEBIG.

(Concluded from our May No.)

RELATIONS BETWEEN THE VARIOUS PROPERTIES OF BODIES.-CONNEXION OF VITAL PROPERTIES WITH CHEMICAL.-NECESSITY FOR ANATOMY; ITS INSUFFICIENCY. -CHEMISTRY NECESSARY, BUT INSUFFICIENT.-ILLUSTRATIONS.-VALUE OF 1 CHEMICAL FORMULE.-CONCLUSION.

The Law of the Relations of Mutual Dependence existing between two phenomena independently of the causes producing these phenomena.

The examples adduced in the preceding paper clearly demonstrate the existence of a natural law, and show that the properties of a body stand in a definite relation to its composition, and that an alteration in one of the properties of a body is attended with a corresponding alteration in some one of its quantitative relations. What deserves particular notice here is, that the knowledge of, this natural law, of the mutual relation between the boiling point of substances and their composition, is altogether independent of the actual cause, or of the conditions, to the joint operation of which the constancy of the respective boiling point of substances is to be ascribed, since the real nature of the boiling point is as much unknown to us as the real nature of life.

The Mutual Dependence of Composition, Specific Gravity, and the Boiling Point.

Every property of bodies stands in some similar relation to their composition, as the boiling point of the foregoing example. A law has been made out for a considerable number of organic bodies, which enables us, from a knowledge of the boiling point, to deduce the weight of a cubic foot of any of these substances; consequently, it appears that the specific gravity of bodies—that is, the pressure exerted by equal volumes on a substratum supporting them, stands in a definite relation to, and varies with variations of, two other propertiesnamely, their boiling point and their composition.

Relation between Specific Gravity and Atomic Weight.

A similar relation of dependence has been discovered to exist between the respective amounts of heat required to raise the temperature of bodies to the same point, and the relative weights in which they enter into combination, (equivalents.) It is a well known fact, that different bodies at the same temperature contain different quantities of heat. Equal weights of sulphur, iron, and lead, for example, heated to 212°, when placed in contact with ice, melt widely different quantities of the latter. Now, if the amount of heat in these

bodies were equal, it is obvious the amount of ice liquefied would in every case be equal. The differences in this respect manifestly indicate differences in the cause of the liquefaction. The sulphur liquefies six and a half times, the iron four times, as much ice as the lead. If we heat equal weights of sulphur, iron, and lead, to the same extent-say from 60° to 400°-with the same spirit-lamp, it is obvious, that if for a given weight of lead half an ounce of spirits, be necessary, then, for the same weight of sulphur, three and a quarter, and for iron, two ounces, would be consumed. These different amounts of heat required to heat to the same temperature various bodies, are on this account termed specific heats. From a knowledge of the unequal quantities of heat which equal weights of different bodies contain, at the same temperature, we may, by rule of three, calculate the weights of sulphur, iron, and lead, which contain an equal amount of specific heat. From this calculation, it appears that 16 parts of sulphur liquefies as much ice as do 28 parts of iron, or 104 parts of lead, at the same temperature. These numbers correspond exactly to the equivalents of sulphur, iron, and lead. So that the equivalents of these and other bodies coincide with like quantities of heat; in other words, require like quantities to raise them to the same temperature. If we consider that the equivalents of bodies represent the relative weights of the atoms, it is evident that the quantity of heat absorbed or yielded up by every single atom, under like conditions, is the same for every atom, and expressed in figures, is inversely proportionate to the weights of the atoms. It is certainly a curious fact, that the quantity of ice which a body melts should have served to determine and correct in many instances, the combining proportion of that body.

Relation between the Specific Heat and Musical Tone of Gases.

It may appear still more wonderful to many persons, that this property (to absorb or to yield heat) stands, in gaseous bodies, in a definite relation to the sound produced by the transmission of the gas through a pipe or flute; indeed, a celebrated philosopher (DULONG) computed, from the difference in the sound thus produced, the respective quantity of heat evolved by gases upon compression, or absorbed in their expansion. In order to understand clearly this remarkable relation between the specific heat of gases and their power of propagating sound, I may refer to an idea occurring to LA PLACE, which is one of his most beautiful and happy thoughts. It is well known that Newton, and many other mathematicians after him, endeavoured in vain to deduce a formula for the velocity of sound that should exactly correspond with the results of actual observation; they succeeded, indeed, to deduce approximate formulæ, but none that corresponded exactly; there remained invariably an inexplicable difference. Now, as the propagation of sound is effected by the vibrations of the elastic molecules of the air-consequently, by the compression and subsequent expansion of the particles; and as heat is liberated upon the compression, and absorbed upon the expansion, of the atmosphere-La Place conjectured that this phenomena of heat ought to exercise a certain influence upon the propagation of sound; and it was in reality found that the formula which the mathematicians had deduced for the velocity of sound corresponds exactly with the results of actual observation, if the specific heat of the air is taken into account.

Now, if we compute the velocity of sound by the Newtonian formula, (i. e., without taking the specific heat of the air into account,) and compare the result with the formula of La Place, we find between the two a difference in the extent of space which a wave of sound is computed to traverse in a second. This difference in the velocity of the propagation of sound arises from the specific heat of the air, or, in other words, from the quantity of heat evolved from the molecules of air compressed during the passage of the sound. Now, it is obvious that this difference in the velocity of the propagation of sound will, in the case of other gases which with equal volume contain and evolve upon pressure more or less heat that the air, be greater or less than it is in the case of the

atmosphere, and consequently, that the figures expressive of these different velocities of sound in various gases indicate at the same time the different quantities of heat which these gases respectively contain.

Now, since the acuteness or the gravity of tones depends upon the number of vibrations produced by a wave of sound in a second, and consequently upon the velocity with which the motion imparted is propagated, and since we know that the velocity of the propagation of a wave of sound is, in all gases, directly proportionate to the number of vibrations of the tones thereby produced by it,it follows, that from the difference in the height of the tone produced respectively by the transmission of different gases through a pipe, we may determine the respective specific heat of the several gases.

Acoustics owes the rank which it at present occupies amid the sciences to the grand discovery, that musical harmony, that every sound which touches the heart excites us to joy, or inspires us with valour, is the mark and sign of a definite and determinable number of vibrations of the particles of the propagating medium, and thus a sign of everything that may be deduced from this motion according to the laws of undulation. A number of facts concerning tones have been deduced from the theory of undulation; whilst, on the other hand, empirical truths have led to a corresponding knowledge of the properties of vibrating bodies, which properties formerly were entirely unknown.

It is asserted of a celebrated violin-maker of Vienna, that he himself selected the wood for his violins in the forest, making choice of those trees which, under the stroke of a hammer, returned a certain peculiar sound known to himself alone. This, in all probability, is a fable; but there can be no doubt that he knew that the upper and lower boards of a good violin must make a certain number of oscillations in a second, and produce a certain definite sound; and that he ought to be governed by this consideration in the selection of the boards, particularly as to their respective thickness.

Relation between Electricity and Magnetism-Magnetism and Heat-Magnetism and Chemical Force.

If, finally, we take into consideration that the electric current passing through a metallic wire stands in a definite relation to the magnetic properties thereby imparted to the wire-if we recollect that the most minute differences of radiated heat may be measured by the magnetic needle-that the quantity of electricity put in motion is expressible in numbers by means of the same needle -that this quantity may be measured in cubic inches of hydrogen, and weights of metals, and when we thus see that the causes or forces which govern the properties of bodies, their power to make impressions upon our senses, or to produce effects in general, stand in a definite and determinal relation of dependence to one another, how can we doubt that the vital properties likewise obey the same laws of mutual dependence, and that the chemical and physical properties of the elements, their form and mode of arrangement, perform a definite and determinable part in the vital phenomena.

Fallacy of looking upon Vital Properties as exceptions to the Laws of Nature.

The false method pursued by many physiologists and pathologists has led them to look upon the vital properties, in some measure, as exceptions to a great law of Nature. How otherwise can we explain their refusal to look upon the number and arrangement of the elements, which constitute the various parts of the organism, as a physiological property affording an indispensable auxillary towards the ultimate attainment of a clear insight into the vital phenomena! How otherwise can we explain that, in the treatment of diseases, they should neglect to take into account the elementary composition of the remedies, and the properties dependent upon that composition, and through which the curative action is exercised? The mere knowledge of the formulæ, of course, does not suffice for this purpose. It is necessary likewise to ascertain

the laws of the relations in which the composition and form of the food or of the secretions stand to the process of nutrition, and in which the composition of the remedies stand to the action which they exercise upon the organism.

Anatomy essential to the progress of Physiology.

SCHLEIDEN says, "It is unquestionable that all the advances made in the physiology of plants and animals, from the time of ARISTOTLE up to our own days, have been effected mainly through the progress made in anatomy. The mere sight of the mash-tub, the fire, and the pipe, from which the spirit runs, is not sufficient to afford a clear insight into the process of distillation: this requires absolutely an accurate knowledge of the whole apparatus. Now the organism is a much more complicated apparatus than a still, and before we can attempt to judge of the importance and functions of the several parts composing it, it is absolutely necessary that we should acquire a perfectly accurate knowledge of the structure of every individual part.”

But we must not forget here, that from the days of ARISTOTLE to those of LEEUWENHOEK, anatomy has thrown only a partial light upon the laws that govern the vital phenomena; that the mere knowledge of a distillation apparatus does not suffice to inform us of the purpose for which this apparatus is intended, and to instruct us as to its modus operandi; and that he who knows the nature of the fire, the laws of the diffusion of heat, the laws of vaporization, the composition of the mash, and that of the product of the distillation, knows infinitely more of distillation, not only than he who simply knows the apparatus in its most minute details, but infinitely more even than he who constructed the apparatus.

Each new discovery in anatomy has added to the precision, accuracy, and extent of the descriptions of the various parts of the organism, and their functions; unwearied investigation and research has penetrated even to the cell; but from this point our researches must proceed upon a new track.

Anatomy alone insufficient.

But if, as many persons seem to think, the further progress of physiology, both for the present and in future, must entirely depend upon the progressive improvements of our knowledge of the anatomical structures of organisms, then, indeed, chemistry can be of no avail to physiology, since it does not contribute to enlarge our anatomical knowledge, having for its object, not the form, but the relations of the form to the elements, and to their mode of arrangement, by which that form is produced. The study of anatomical structures, and of the relations of the various structures constituting the animal organism, serves exclusively to advance the science of anatomy; and the most minute and accurate research into the motory phenomena affords not the slightest clue to the causes and laws which govern these phenomena. It only teaches us the mode and manner in which the motion is directed.

Chemistry the necessary adjunct of Anatomy in the Solution of Physiological Questions.

If, then, anatomy alone will not enable us to solve physiological questions, it is evident that something besides is required for this purpose; and the first thing, in this respect, must surely be the knowledge of the matter of which the form consists, of the forces and properties which it possesses, besides the vital properties, its origin, and the alteration which it undergoes to acquire vital properties. To this knowledge must be added, as equally indispensable, that of the relations in which all the constituent parts of the organism, both fluid and solid, stand to one another, independently of their form. Many physiologists fancy that the discoveries which chemistry has made regarding these highly important questions, have simply served to enrich the domain of chemistry, although, in reality, all these acquisitions occupy, in chemical science, the same subordinate rank as those gained by the analyses of minerals and of mineral

waters.

Chemistry alone insufficient to explain the Phenomena of Life.

Another fundamental error entertained by another class of physiologists, is to suppose that the chemical and physical forces are in themselves, or in conjunction with anatomy, sufficient to explain the phenomena of life. One would, indeed, hardly believe, that whilst the chemist, who is most intimately acquainted with the chemical forces, recognizes in the living body the existence of new laws and of new forces unknown to him, the physiologists, who claims but a very defective and superficial knowledge of the nature and action of chemical and physical forces, should attempt to explain the vital phenomena by the laws of inorganic matter alone.

The view which would assign this disproportionate share in the vital phenomena to the chemical and physical forces, may be considered as the extreme result of the reaction against another view that preceded it, and which ascribed all the phenomena of the living organism entirely and exclusively to the vital force. Now, on the contrary extreme, some reject the vital force altogether, supposing that all the vital processes are referable to physical and chemical causes. Forty years ago, it was a favourite notion of physiologists to assume the existence, in the living animal body, of laws different from those which govern inorganic nature, and to assert the most perfect dissimilarity between organic processes and those ocurring in inorganic matter. Many of our modern physiologists, on the other hand, would maintain that there exists the most perfect analogy between these two sets of laws and processes. Both these theories are alike untenable; they labour alike under one great and fatal defectviz., the advocates of neither have never endeavoured to establish or determine the differences between the effects of the vital force and those of the inorganic forces, nor their respective similarites or analogies. The deductions and conclusions which were arrived at, were not based upon the knowledge of the points of similarity or dissimilarity which their mutual relations presented, but rather upon a total ignorance of both these points.

True definition of the term " Chemical Forces."

Those physiologists who regard the vital processes as the effects of inorganic forces, forget altogether that the term "chemical forces" implies nothing beyond what is quantitative in the various vital manifestations, and the qualities dependent upon these quantities.

It is entirely owing to the erroneous notions entertained of the influence which chemistry exercises in the vital phenomena, that this influence is, on the one side, greatly underrated, whilst, on the other side, the expectations entertained of, and the demands made upon chemistry, are exaggerated.

Numbers serve simply to express fully established relations of mutual dependence between two or several facts, but not to establish such relations.

When a definite relation has been discovered to exist between two facts, it is by no means the task of chemistry to demonstrate their relation, but simply to express it quantitatively, or in numbers. But these numbers themselves do not constitute or establish any relation between two facts, if such relation does not really exist.

Oil of bitter almonds and benzoic acid are, in origin and properties, two totally different organic compounds. A few years ago the existence of a mutual relation between these two substances was not even thought of. But when it was discovered that oil of bitter almonds becomes solid and crystaline upon exposure to the air, and that the resulting body is identical in properties and composition with benzoic acid, this fact placed the existence of a relation between these two substances at once beyond question. Subsequent observations and examinations showed that oxygen is absorbed from the atmosphere upon the transformation of the bitter almond oil into benzoic acid, and the formula deduced from the respective analysis of both substances expressed this transformation in figures, and explained it thus so far as it admitted of explanation.

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