The right of Translation is reserved.
JOHN OniLDS AND SON. TKINTERS.
PEEFACE.
The aim of tMs work is to set forth the genei^al truths of Biology, as illustrative of, and as interpreted by, the laws of Evolution: the special truths being introduced only so fai' as is needful for elucidation of the general truths.
For aid in executing it, I owe many thanks to Prof. Huxley and Dr Hooker. They have supplied me with in- formation where my own was deficient; and in looking through the proof-^^heets, have pointed out errors of detail into which I had fallen. By having kindly rendered me this valuable assistance, they must not, however, be held committed to any of the enunciated doctrines that are not among the recognized truths of Biology.
The successive instalments which compose this volume, were issued to the subscribers at the following dates: — No. 7 (pp. 1—80) in January, 1863; No. 8 (pp. 81—160) in April, 1863; No. 9 (pp. 161—240) in July, 1863; No. 10 (pp. 241—320) in January, 1864; No. 11 (pp. 321—400) in May, 1864; and No. 12 (pp. 401—476) in October, 1864.
London, Sejptenfiber 29th, 1864.
f \l CONTENTS OF VOL L PAET I.— THE DATA OF BIOLOGY.
CHAP. PAGE II. — THE ACTIONS OF EORCES ON ORGANIC MATTER.. 25 III. — THE RE-ACTIONS OF ORGANIC MATTER ON FORCES 42 IV. — PROXIMATE DEFINITION OF LIFE...59 V. — THE CORRESPONDENCE BETWEEN LIFE AND ITS CIR- CUMSTANCES...72 VI. — THE DEGREE OF LIFE VARIES AS THE DEGREE OF CORRESPONDENCE...82 VII. — THE SCOPE OF BIOLOGY...94 PAET II.— THE INDUCTIONS OF BIOLOGY.
I. — GROWTH II. — DEVELOPMENT III. FUNCTION IV. — WASTE AND REPAIR V. — ADAPTATION,.
vm CONTENTS.
CHAP.
VI. — INDIVIDUALITY VII. — GENESIS VIII. HEEEDITT IX. — VARIATION X.— GENESIS, HEREDITY, AND VARIATION XI. — CLASSIFICATION XII. — DISTRIBUTION PAET III.— THE EVOLUTION OF LIFE.
II. — GENERAL ASPECTS OF THE SPECIAL-CREATION-HY- POTHESIS...333 III. — GENERAL ASPECTS OF THE EVOLUTION-HYPOTHESIS 346 IV. — THE ARGUMENTS FROM CLASSIFICATION.. 356 V. THE ARGUMENTS FROM EMBRYOLOGY...365 VI. — THE ARGUMENTS FROM MORPHOLOGY...380 VII. — THE ARGUMENTS FROM DISTRIBUTION...388 VIII. — HOW IS ORGANIC EVOLUTION CAUSED?...402 IX. — EXTERNAL FACTORS...411 XI. — DIRECT EQUILIBRATION...432 XII. — INDIRECT EQUILIBRATION...443 XIII. — THE CO-OPERATION OF THE FACTORS...464 XIV. — THE CONVERGENCE OF THE EVIDENCES...470 PART I.
THE DATA OF BIOLOGY.
I CHAPTER I.
ORGANIC MATTER.
§ 1. Of the four chief elements whicli, in various com- binations, make up living bodies, three are gaseous. While carbon is known only as a solid, oxygen, hydrogen, and nitrogen are known only in the aeriform state. Under pressures great enough to reduce them almost to the density of liquids these elements have still defied all efforts to liquefy them. There is a certain significance in this. When we. remember how those re- distributions of Matter and Motion which constitute Evolution, structural and functional, imply motions in the units that are re-distributed; we shall see a probable meaning in the fact that organic bodies, which exhibit the phenomena of Evolution in so high a degree, are mainly composed of ultimate units having extreme mobility. The properties of substances, though destroyed to sense by combination, are not destroyed in reality: it follows from the persistence of force, that the properties of a compound are resultants of the properties of its components — resultants in which the properties of the components are severally in full action, though greatly obscured by each other. One of the leading properties of each substance is its degree of molecular mobility; and its degree of molecular mobility more or less sensibly affects the molecular mobilities of the various compounds into which it enters. Hence we may infer some relation between the gaseous form of three out of the four 4 THE DATA OF BIOLOGY.
chief organic elements, and that comparative readiness dis- played by organic matters to undergo those changes in the arrangement of parts which we call development, and those transformations of motion which we call function.
Considering them chemically instead of physically, it is to be remarked that three out of these four main components of organic matter, have affinities which are narrow in their range and low in their intensity. Hydrogen combines with comparatively few other elements; and such chemical energy as it does show, is scarcely at all shown within the limits of the organic temperatures. Of carbon it may similarly be said that it is totally inert at ordinary heats; that the number of substances with which it unites is not great; and that in. most cases its tendencv to unite with them is but feeble. Lastly, this chemical indifference is shown in the highest degree by nitrogen — an element which, as we shall here- after see, plays the leading part in organic changes.
Among the organic elements, including under the title not only the four chief ones, but also the less conspicuous re- mainder, that capability of assuming different states, called allotropism, is frequent. Carbon presents itself in the three unlike conditions of diamond, graphite, and charcoal. Under certain circumstances, oxygen takes on the form in which it is called ozone. Sulphur and phosphorus (both, in small proportions, essential constituents of organic matter) have allotropic modifications. Silicon, too, is allotropic; whilo its oxide, silica, which is an indispensable constituent of many lower organisms, exhibits the analogue of allotropism • — isomerism. And even of the iron which plays an active part in higher organisms, and a passive part in some lower ones, it may be said that though not known to be itself allo- tropic, yet isomerism characterizes those compounds of it that are found in living bodies. Allotropism being interpre table as some change of molecular arrangement, this frequency of its occurrence among the components of organic matter, is significant as implying a further kind of molecular mobility.
ORGANIC MATTER. 5^ One more fact, that is here of great interest for us, must be set down. These four elements of which organisms are almost wholly composed, present us with certain extreme antitheses. While between two of them we have an unsur- passed contrast in chemical activity; between one of them and the other three, we have an unsurpassed contrast in molecular mobility. While carbon, by successfully resisting fusion and volatilization at the highest temperatures that can be produced, shows us a degree of atomic cohesion greater than that of any other known element, hydrogen, oxygen, and nitrogen, show the least atomic cohesion of all elements. And while oxygen displays, alike in the range and intensity of its affinities, a chemical energy exceeding that of any other substance (unless fluorine be considered an exception), nitrogen displays the greatest chemical inactivity, Now on calling to mind one of the general truths arrived at when analyzing the process of Evolution, the probable significance of this double difference will be seen. It was shown {First Principhs^ § 123) that, other things equal, unlike units are more easily separated by incident forces than like units are — that an inci- dent force falling on units that are but little dissimilar does not readily segregate them; but that it readily segregates them if they are widely dissimilar. Thus, these two extreme contrasts, the one between physical mobilities, and the other between chemical activities, fulfil, in the highest degree, a certain further condition to facility of differentiation and in-, tegration, § 2. Among the binary combinations of these four chief organic elements, we find a molecular mobility much less than that of these elements themselves; at the same time that it is much greater than that of binary compounds in general. Of the two products formed by the union of oxygen with carbon, the first, called carbonic oxide, which contains one atom of carbon to one of oxygen (expressed by the symbol C 0), is an incondensible gas; and the second 6 THE DATA OF lUOLOGY.
carbonic acid, containing an additional atom of oxygen (C O2) assumes a liquid form only under a pressure of nearly forty atmospheres. The several compounds of oxygen with nitrogen, present us with an instructive gradation. Protoxide of nitrogen, which contains one atom of each element (N 0), is a gas condensible only under a pressure of some fifty at- mospheres; deutoxide of nitrogen (N O2) is a gas hitherto uncondensed (the molecular mobility remaining undiminished in consequence of the volume of the united gases remaining unchanged); nitrous acid (N O3) is gaseous at ordinary temperatures, but condenses into a very volatile liquid at the zero of Fahrenheit; peroxide of nitrogen (N O4) is gaseous at 7P, liquid between that and 16*', and becomes solid at a tem- perature below this; while nitric acid (N O3) may be obtained in crystals which melt at 85** and boil at 113°. In this series we see, though not with complete uniformity, a de- crease of molecular mobility as the weights of the compound molecules are increased. The hydro- carbons illustrate the same general truth still better. One series of them will suffice. Marsh gas (C2 HJ is permanently gaseous, defiant gas (C4 H4) may be liquefied by pressure. Oil gas, which is identical with defiant gas in the proportions of its constituents but has double the atomic weight, (Cg Ilg), becomes liquid without pressure at the zero of Fahrenheit. Amylene (CioHio) is a liquid which boils to 102*^. And the suc- cessively higher multiples, caproylene (C12 Hia)? caprylene (C16 Hie), elaene (Cig His) ^^d paramylene (C20 H20), are liquidsi which boil respectively at 102% 13P, 257°, 230°, and 329°. Cetylene (C32 H32) is a liquid which boils at 527°; while pa- raffine (C54 H54) and mylene (Cgo Hr,o) are solids. Only one compound of hydrogen with nitrogen has been obtained in a free state — ammonia (H3 N); and this, which is gaseous, is liquefiable by pressure, or by reducing its temperature to — 40° F. In cyanogen, which is composed of nitrogen and carbon (N C2), we have a gas that becomes liquid at a pressure of four atmospheres and solid at — 30° F. And, in ORGANIC MATTER. / paracyanogen, formed of the same proportions of these ele- ments in higher multiples (N3 Cg), we have a solid which does not fuse or volatilize at ordinary temperatures. Lastly, in the most important member of this group, water, (H 0 or else as many chemists now think II2 O2) we have a com- pound of two incondensible gases which assumes both tha fluid state and the solid state within ordinary ranges of temperature; while its molecular mobility is still such that its fluid or solid masses are continually passing into the form of vapour, though not with great rapidity until the temper- ature is raised to 212".* Considering them chemically, it is to be remarked of these binary compounds of the four chief organic elements, that they are, on the average, less stable than binary com- pounds in general. Water, carbonic oxide, and carbonic acid, are, it is true, difficult to decompose. But omitting these, the usual strength of union among the elements of the above-named substances is low considering the simplicity' * This immense loss of molecular mobility which oxygen and hydrogen un- dergo on uniting to form water — a loss far greater than that seen in other binaiy compounds of analogous composition — suggests the conclusion that the atom of water is a multiple atom. Thinking that if this conclusion be true, some evidence of the fact must be afforded by the heat -absorbing power of aqueous vapour, I lately [put the question to Prof. Tyndall, whether it resulted from his ex- periments that the vapour of water absorbs more heat than the supposed sim- plicity of its atom would lead him to expect. I learned from him that it has an excessive absorbent power — an absorbent power more like that of the complex- atomed vapours than like that of the simple-atomed vapours — an absorbent power that therefore harmonizes with the supposition that its atom is a multiple one. Besides this anomalous loss of molecular mobility and this anomalous heat- absorbing power, there are other facts which countenance the supposition. The unparalleled evolution of heat during the combination of oxygen and hydrogen is one. Another is that exceptional property which water possesses, of beginning to expand when its temperature is lowered below 40^; since this exceptional property is explicable only on the assumption of some change of molecular arrangement — a change which is comprehensible if the molecules are multiple ones. And yet a further confirmatory fact is the ability of water to assume a colloid condition; for as this implies a capacity in its atoms for aggregating into high multiples, it suggests, by analogy with known cases, that they have a capacity for aggregating into lower multiples.
S, THE DATA OF BIOLOGY.
of the substances. With the exception of acetylene, the various hydro-carbons are not producible by directly com- bining their elements; and the elements of most of them are readily separated by heat without the aid of any antagonistic affinity. Nitrogen and hydrogen do not unite with each other immediately; and the ammonia whicn results from their mediate union, though it resists heat, yields to the electric spark. Cyanogen is stable: not being resolved into its components at a red heat, unless in iron vessels. Much less stable however are the several oxides of nitrogen. The protoxide, it is true, does not yield up its elements below a red heat; but nitrous acid cannot exist if water be added to it; hypo-nitric acid is decomposed both by water and by contact with the various bases; and nitric acid not only readily parts with its oxygen to many metals, but when anhydrous, spontaneously decomposes. Here it will be well to note, as having a bearing on what is to follow, how characteristic of most nitrogenous compounds is this special instability. In all the familiar cases of sudden and violent decomposition, the change is due to the presence of nitrogen. The explosion of gunpowder results from the readiness with which the nitrogen contained in the nitrate of potash, yields up the oxygen combined with it. The explosion of gun-cot- ton, which also contains nitric acid, is a substantially par- allel phenomenon. The various fulminating salts are all formed by the union with metals, of a certain nitrogenous acid called fulminic acid; which is so unstable that it cannot be obtained in a separate state. Explosiveness is a property of nitro-mannite, and also of nitro- glycerin. Iodide of nitrogen detonates on the slightest touch, and often without any assign- able cause. Percussion produces detonation in sulj^hide of nitrogen. And the bod}^ which explodes with the most tremendous violence of any that is known, is the chloride of nitrogen. Thus these easy and rapid decompositions, due to the chemical indifference of nitrogen, are characteristic. When we come hereafter to observe the part which nitrogen ORGANIC MAITER. 9 ORGANIC MAITER. 9 plays in organic actions, we shall see the significance of this extreme readiness shown by its compounds to undergo change. Returning from these facts parenthetically introduced, we have next to note that though among these binary compounds of the four chief organic elements, there are a few active ones, yet the majority of them display a smaller degree of chemical energy than the average of binary compounds. Water is the most neutral of bodies: usually pro- ducing little chemical alteration in the substances with which it combines; and being expelled from most of its combinations by a moderate heat. Carbonic acid is a relatively feeble acid: the carbonates being decomposed by the majority of other acids and by ignition. The various hydro-carbons are but narrow in the range of their comparatively weak affinities. The compounds formed by ammonia have not much stability: they are readily destroyed by heat, and by the other alkalies. The affinites of cj^anogen are tolerably strong; though they yield to those of the chief acids. Of the several oxides of ni- trogen it is to be remarked, that while those containing the smaller proportions of oxygen are chemically inert, that con- taining the'greatest proportion of oxygen (nitric acid) though chemically active, in consequence of the readiness with which one part of it gives up its oxygen to oxidize a base with which the rest combines, is nevertheless driven from all its combinations by a red heat.
These binary compounds, like their elements, are to a con- siderable degree characterized by the prevalence among them of allotropism; or, as it is more usually called when displayed by compound bodies — isomerism. Professor Graham finds reason for thinking that a change in atomic arrange- ment of this nature, takes place in water, at or near the melting point of ice. The relation between cj^anogen and paracyanogen is, as we saw, an isomeric one. In the above- named series of hydro-carbons, differing from each other only in the multiples in which the elements are united, we find isomerism becoming what is distinguished as polymerism.
10 THE DATA OF BIOLOGY.
The like is still more conspicuous in other groups of the hydro-carbons, as in the essential oils: sixteen to twenty of which are severally isomeric with essential oil of turpentine. Here the particular kind of molecular mobility implied by these metamorphoses, is well shown: essential oil of turpen- tine being converted into a mixture of several of these poly- merides, by simple exposure to a heat of 460".
There is one further fact respecting these binary compounds of the four chief organic elements, which must not be over- looked. Those of them which form parts of the living tissues of plants and animals (excluding water which has a me- chanical function, and carbonic acid which is a product of decomposition) are confined to one group — the hydro-carbons. And of this group, which is on the average characterized by comparative instability and inertness, these hydro-carbons found in living tissues, are among the most unstable and inert.
§ 3. Passing now to the substances which contain three of these chief organic elements, we have first to note that along with the greater atomic weight which mostly accom- panies their increased complexity, there is, on the average, a further marked decrease of molecular mobility. Scarcely any of them maintain a gaseous state at ordinary temperatures. One class of them only, the alcohols and their derivatives, evaporate under the usual atmospheric pressure; but not rapidly unless heated. The fixed oils, though they show that molecular m.obility implied by an habitually liquid state, show this in a lower degree than the alcoholic compounds; and they cannot be reduced to the gaseous state without de- composition. In their allies, the fats, which are solid unless heated, the loss of molecular mobility is still more marked. And throughout the whole series of the fatty acids, in which to a fixed proportion of oxygen there are successively added higher equimultiples of carbon and hydrogen, we see how tlie molecular mobility decreases with the increasing sizes of Olio AN I C MATTKR. 11 the atoms. In the amylaceous and saccharine group of com- pounds, solidity is the habitual state: such of them as can assume the liquid form, doing so only when heated to 300" or 400'' F.; and decomposing when further heated, rather than become gaseous. Eesins and gums exhibit general physical properties of like character and meaning.
In chemical stability these ternary compounds, considered as a group, are in a marked degree below the binary ones. The various sugars and kindred bodies, decompose at no very high temperatures. The oils and fats are also readily carbon- ized by heat. Resinous and gummy substances are easily made to render up some of their constituents. And the alcohols w4th their allies, have no great power of resisting decomposition. These bodies, formed by the union of oxygen, hydrogen and carbon, are also, as a class, chemically inactive. The formic and acetic are doubtless energetic acids; but the higher members of the fatty-acid series are easily separated from the bases with which they combine.* Saccharic acid, too, is an acid of considerable power; and sundry of the vegetal acids possess a certain activity, though an activity far less than that of the mineral acids. But throughout the rest of the group, there is shown but a small tendency to combine with other bodies; and such com- binations as are formed have usually little permanence.
The phenomena of isomerism and polymerism are of fre- quent occurrence in these ternary compounds. Starch and dextrine are isomeric. Fruit sugar, starch sugar, eucalyn, sorbin, and inosite, are polymeric. Sundry of the vegetal acids exhibit similar modifications. And among the resins and gums, with their derivatives, molecular re-arrangements of this kind are not uncommon.
One further fa3t respecting these compounds of carbon, oxygen and hydrogen, should be mentioned; namely, that they are divisible into two classes — the one consisting of sub- stances that result from the destructive decomposition of organic matter, and the other consisting of substances that 12 THE DATA OF BIOLOGY.
exist as such in organic matter. These two classes of sub- stances exhibit in different degrees, the properties to which we have been directing our attention. The lower alcohols* their allies and derivatives, which possess greater molecular mobility and chemical stability than the rest of these ternary compounds, are not found in animal or vegetal bodies. While the sugars and amylaceous substances, the fixed oils and fats, the gums and resins, which have all of them much less mole- cular mobility, and are, chemically considered, more unstable and inert, are components of the living tissues of plants and animals.
§ 4. Among compounds containing all the four chief organic elements, a division analogous to that just named may be made. There are some which result from the decom- position of living tissues; there are others which make parts of living tissues in their state of integrity; and these two groups are contrasted in their properties in the same way as are the parallel groups of ternary compounds.
Of the first division, certain products found in the animal excretions are the most important, and the only ones that need be noted; such, namely, as urea, kreatine, kreatinine. These animal bases exhibit much less molecular mobility than the average of the substances treated of in the last section: being solid at ordinary temperatures, fusing, where fusible at all, at temperatures above that of boiling water, and having no power to assume a gaseous state. Chemically considered, their stability is low, and their activity but small, in com- parison with the stabilities and activities of the simpler com- pounds.
It is, however, the nitrogenous constituents of living tis- sues, that display most markedly, those characteristics of which we have been tracing the growth. Albumen, fibrin, casein, and their allies, are bodies in which that molecular mobility exhibited by three of their components in so high a degree, is reduced to a minimum. These substances are known only ORGANIC MATTER. 13 ORGANIC MATTER. 13 in the solid state: that is to say, when deprived of the water usually mixed with them, they do not admit of fusion, much less of volatilization. To which add, that they have not even that molecular mobility which solution in water implies; since, though they form viscid mixtures with water, they do not dissolve in the same perfect way as do inorganic com- pounds. The chemical characteristics of these sub- stances, are instability and inertness carried to the extreme. How rapidly albumenoid matters decompose under ordinary conditions, is daily seen: the difficulty of every house-wife being to prevent them from decomposing. It is true that when desiccated and kept from contact with air, they may be preserved unchanged for a long period; but the fact that they can only be thus preserved, proves their great instability. It is true, also, that these most complex nitrogenous principles are not absolutely inert; since they enter into combinations with some bases; but their unions are very feeble.
It should be noted, too, of these bodies, that though they exhibit in the lowest degree that kind of molecular mobility, which implies facile vibration of the atoms as wholes, they ex- hibit in a high degree that kind of molecular mobility resulting in isomerism, which implies permanent changes in the posi- tions of adjacent atoms with respect to each other. Each of them has a soluble and insoluble form. In some cases there are indications of more than two such forms. And it appears that their metamorphoses take place under very slight changes of conditions.
In these most unstable and inert organic compounds, we find that the atomic complexity reaches a maximum: not only since the four chief organic elements are here united with small proportions of sulphur and phosphorus; but also since they are united in high multiples. The peculiarity which we found characterized even binary compounds of the organic elements, that their atoms are formed not of single equivalents of each component, but of two, three, four and more equivalents, is carried to the greatest extreme in these 14 THE DATA OF BIOLOGY.
compounds, that take the leading part in organic actions, According to Mulder, the formula of albumen is 10 (C^° H^^ N' 0^^) 4- S^ P- That is to say, with the sulphur and phos- phorus there are united ten equivalents of a compound atom containing forty atoms of carbon, thirty-one of hydrogen, five of nitrogen, and twelve of oxygen: the atom being thus made up of nearly nine hundred ultimate atoms.
§ 5. Did space permit, it would be useful here to consider in detail, the interpretations that may be given of the pecu- liarities we have been tracing: bringing to their solution, those general mechanical principles which are now found to hold true of molecules as of masses. But it must sufiice briefly to indicate the conclusions that such an inquiry pro- mises to bring out.