The Fitness of the Environment

ditions in the environment ; number, variety, complexity, adaptability, availability, activity, and richness in energy of the substances which take part in the metabolic processes and in the chemical and physical formation of the organism ; constancy of physico-chemical con- ditions, such as temperature, alkalinity, col- loidal disperseness, etc., within the organism; the ejQSciency of many physiological processes ; the availability of electrical forces, etc.

In short, by many independent and united actions the above catalogued natural char- acteristics of the environment promote and favor complexity, regulation, and metabo- lism, the three fundamental characteristics of life upon which all our discussion has been based. One manner of judging the completeness with which different types of phenomena and properties, different elements and compounds, have been considered in the descriptive chap- ters preceding is to glance at the several departments of physical science, — chemistry, mechanics, heat, sound, light, magnetism, elec- tricity, and physical chemistry.

In setting out to consider physical and chemical properties we may perhaps begin with chemical phenomena in the narrowest sense. Such phenomena, depend, according to the atomic theory, upon rearrangements of atoms within molecules. They result in the conversion of individual substances into one another, and they are accompanied by rearrangements of energy. In the first place, it is to be noted that enormous quantities of carbon, hydrogen, and oxygen, as water and carbonic acid, are, during a very long period of time, apparently inevitable constituents of the atmosphere of an astronomical body of sufficient size, after cooling has led to the formation of a crust. Further, it has been shown that in number, variety, complexity of forms and changes, and in the magnitude of the accompanying trans- formations of energy the known substances made up of carbon and hydrogen, and those made up of carbon, hydrogen, and oxygen far surpass the compounds of any other elements. Likewise the known compounds of oxygen and hydrogen with other elements are. the most numerous and important among inorganic substances. Two peculiarities of the carbon compounds, the formation and properties of the carbohydrates, and the nature of the pro-

cess known as hydrolytic cleavage, add to this list of chemical characteristics which make for fitness. These facts appear to indicate that in gen- eral chemical behavior, in certain special characteristics as well, and in the magnitude of the quantity of energy rendered available by their chemical changes, the elements car- bon, hydrogen, and oxygen are uniquely and most highly fitted to be the stuff of which life is formed and of the environment in which it exists.

Mechanics has taken a place subordinate to chemistry in the present work. Neverthe- less, it has been noted that the unique proper- ties of water are the cause of the admirable mobility of that substance and of the whole environment, and therefore of the dynamical processes of geology, meteorology, etc., in- cluding soil formation ; that it is surface ten- sion which holds water in the soil ; that the eflScacy of water as a means of dissolving the greatest variety of substances in the greatest amounts, makes possible high osmotic pres- sures, as well as mobility of all the elements ; and there are a host of other considerations which have been discussed above. In all such cases the properties of water have been found to be favorable influences for the wel-

fare of the organism. Considering the com- parative unimportance of mechanics in rela- tion to the fundamental postulates, it seems clear that this department has not been over- looked. Thermal processes and thermal effects are perhaps more conspicuous in the table. The thermochemical characteristics of organic com- pounds and the thermal properties of water are all very favorable to life. Stores of heat for the organism, constancy of temperature of both organism and environment, the per- manence of bodies of water, and a multitude of other most important results flow from these properties and bear witness to their unique fitness.

Sound, light, and magnetism have not been considered, for they appear to bear only a secondary relation to the fundamental postu- lates. In electricity no phenomena are more im- portant than those of ionization in solution. To bring about ionization and thus make possible electrochemical processes, water is the very best medium, and the possibility of such processes is probably necessary to the organic mechanism. In addition to the topics of physical chem- istry already referred to under chemistry

and the several departments of physics, the colloids and the ions of hydrogen and hydroxyl remain to be mentioned. It has been shown that the properties of water are exceptionally favorable to the existence and stability of colloidal systems ; also that the properties of carbonic acid result in automatic regulation of the cohcentration of hydrogen and hydroxyl ions in the ocean and in the organism. So far, then, as It is possible to judge by telling over the departments of physical science, our examination of physical and chem- ical properties has not been incomplete.

This conclusion may be further tested with the help of the ideas which underlie Willard Gibbs's " Phase Rule." ^ According to this rule, the condition of equilibrium in any material system depends upon the number of its com- ponents, the number of its phases, temperature, pressure, and, in general, the concentrations of all the components. Without entering upon an explanation of the exact mathemat- ical notions which determine the meaning of the terms " component " and " phase " it will here suflBce to say that in general the number of components increases as the num- ber of separate chemical individuals increases,

1 See, for instance, Findlay, "The Phase Rule and its Applications." London, 1911, 3d ed. and that a phase is any solid, liquid, or gas- eous part of the whole system which possesses homogeneity of composition. For instance, if a system is made up of sand, salt solution, ice, and aqueous vapor, each of these separate parts, in that it is homogeneous, is a phase. Now the properties of water have the result that more readily than other substances it exists simultaneously and in large quanti- ties in the three phases of solid, liquid, and gas as ice, water, and aqueous vapor. This depends upon the high latent heats of fusion and vaporization, the high freezing point of water, and its vapor tension. Water en- hances the complexity of the environment, and is one principal factor in the mobility of the environment as a whole. Further, it makes for stability ; other things being equal, the greater the number of phases, the less the tendency to change. Among phases the dis- perse colloidal type is unique and of very great importance — almost the sole basis, indeed, of great physical complexity — and, as above shown, the peculiar properties of water highly favor the colloidal condition.

The solvent power of water much increases the number of components which may enter into a system of which it is a part ; hence the large number of components of sea water. blood plasma, etc. The variety of compounds, both organic and inorganic, which contain carbon, hydrogen, or oxygen also causes enor- mous increase in the number of components of biological systems like, protoplasm. The effects of the properties of water above enumerated to regulate temperature are almost too numerous to mention. The specific heat of water, its latent heats of fusion and vapori- zation, and the high freezing point all con- tribute to the restriction of temperature range within the organism, in the waters, and over the whole surface of the earth. The vapor pressure of water has been shown to possess great and exceptional variability with change of temperature. This is the most impor- tant property of water meteorologically, and is the necessary condition for its ample cir- culation. The ratio between the gas pressure of carbonic acid and its concentration in water (absorption eoeflScient) has been shown to be the great factor in establishing the mo- bility of that substance. The total atmos- pheric pressure has not entered into our dis- cussion, for it seems to have no important special relation to the properties of the three elements.

In short, the properties of water and of the carbon compounds provide for number, va- riety, and complexity of phases and compo- nents, and for constancy of temperature, while equally important and unique relationships between the properties of water and carbonic acid and their vapor or gas pressures exist, and exert much influence upon the meteoro- logical cycle. Thus, judged by the phase rule, the actual characteristics of the environment may be shown to contribute the factors which make for complexity and regulation of material sys- tems. Now there can be no doubt that, when feasible, the ideal method — from the physico- chemical point of view — to describe a ma- terial system is in the terms of the phase rule.^ Hence the characteristics which that

* "Ten years after the law of mass action was propounded by Guldberg and Waage, Willard Gibbs, Professor of Physics in Yale University, showed how, in a perfectly general manner, free from all hypothetical assumptions as to the molecular condition of the participating substances, all cases of equi- librium could be surveyed and grouped into classes, and how similarities in the behavior of apparently different kinds of systems, and differences in apparently similar systems, could be explained.

" As the basis of his theory of equilibria, Gibbs adopted the laws of thermodynamics, a method of treatment which had first been employed by Horstmann. In deducing the law of equilibrium, Gibbs regarded a system as possessing only three independently variable factors — temperature, pressure, and the concentration of the components of the system — and he enunciated the general theorem now usually known as the rule contemplates are in certain respects the most important of characteristics. Accord- ingly the above test is a valuable indication of the adequacy of the preceding analysis of physical and chemical properties.

In order if possible to discover the nature of such properties of matter as may have been omitted in our study of fitness, I have ex- amined the index of Landolt and Bornstein's " Physikalisch-chemischen Tabellen," a very extensive and comprehensive work. In addi- tion to information regarding the arbitrary units of physical science, I find mention of the following properties which have not been considered in the present discussion: — Phase Rvle, by wliich he defined the conditions of equilibrium as a relationship between the number of what are called the phases and the components of the system." — Findlay, "The Phase Rule and its Applications." London, 1911, 3d ed., p. 8.

It is clear that in the present state of knowledge the consideration of most of these properties is uncalled for. However, it may perhaps be noted in passing that the com- pressibility of water is remarkably small, that of protoplasm even less.^ Hence even great changes in pressure do not readily damage the organism, and, indeed, a frog's muscle appears to function normally after undergoing a pressure of 500 atmospheres.^ Further, it is of decided consequence for many reasons that the optical properties of water are such

* Henderson, Leland, and Means, American Journal of Physiology, XXn, 48, 1908. that light readily penetrates it to considerable depths. As for color, landscape and modern chemical industry alike testify to the availa- bility of carbon compounds as its source. A final test of thoroughness may be based upon a consideration of other compounds and elements. Accepting the decision that no other properties can be so important to an active, complex, and, regulated mechan- ism as those possessed nearly or quite as maxima by water, carbonic acid, and the compounds of the three elements, what are the possibilities of obtaining the same char- acteristics from other substances ?

So far as chemical substances are now known, the only compound which can be even considered on this score as a substitute for water in the environment is ammonia, and in many respects, no doubt, ammonia might serve as well.^ However, chemical processes ' A full discussion of the properties of ammonia which qual- ify it as a substitute for water in the r61e of solvent and other- wise will be found in the article by E. C. Franklin, "The Ammonia System of Acids, Bases, and Salts," American Chem- ical Journal, Vol. 47, p. 285, 1912. In this paper the re- sults of a long series of investigations are brought together. Especially important for the present purpose are the intro- ductory remarks. "The many striking analogies between liquid ammonia and water as electrolytic solvents have been emphasized by the writer and his co-workers in papers which have appeared from time to time during the past decade. In

being what they are, it is impossible to im- agine the presence of vast amounts of am- monia in an atmosphere, while the loss of the greater part of the energy which can be stored by tearing apart hydrogen and oxygen would be a very serious difficulty; but the loss of substantially all the incomparable chemical activity of oxygen is to all appear- ances an insurmountable obstacle to the sub- stitution of ammonia for water in biological processes.

From time to time, loose discussion has arisen among chemists as to the possibility of substituting another element for carbon in the organic cycle. Such speculations have never been serious, but they have at least all those properties which, give to water its unique position among solvents, such as its abnormally high boiling poiat, its high specific heat, its high heat of volatiUzation, its high critical temperature and pressure, its high association con- stant, -its high dielectric constant, and its low boiling-point elevation constant, its power as an electrolytic solvent, and the facility with which it forms compounds with salts, liquid ammonia shows a remarkable similarity to water."

" While the boiling point of liquid ammonia is 33.46° below zero, it stiU appears abnormally high when compared with the boiling temperatures of phosphine, arsine, stibine, me- thane, ethylene, hydrogen sulphide, hydrochloric acid, etc. The specific heat of liquid ammonia and the heat of fusion of the solid are greater than the corresponding constants for water or any other known substance, while its heat of volatilization, with the one exception of water, is the highest

demonstrated that very few elements, prob- ably only silicon, and perhaps boron, can even be imagined in such a r6Ie. It has, moreover, just been shown that there are many facts leading to the conclusion that only carbon among elements, and carbon itself* only in conjunction with hydrogen, has the power to form the skeletons of compounds numerous, complex, and varied like those of organic chemistry. But, apart from this conclusion, it is certain that silicon and boron could not be mobilized like carbon. Quartz,

of any known liquid. The critical temperature of ammonia is abnormally high, and its critical pressure — the more char- acteristic constant — is higher than that of any other liquid exceptLQg water. Ammonia is an associated liquid, and its dielectric constant, though much below that of water, is still high when compared with that of non-electrolytic solvents. Its boiling-point elevation constant is the lowest of any known liquid, namely 3.4, as compared with 5.2 for water. In its tendency to unite with salts and other compounds, it probably exceeds water, since salts with ammonia of crystal- lization are perhaps even more numerously recorded in the literature than are salts with water of crystallization. As a solvent for salts it is generally much inferior to water, though some salts, for example the iodides and bromides of mercury, lead, and silver, dissolve very much more abundantly in ammonia than they do in water, and it far surpasses the latter solvent in its ability to dissolve the compounds of carbon. Finally it exhibits conspicuous power as an ionizing solvent, the more dilute ammonia solutions at 33.5° being very much better conductors of electricity than aqueous solutions of the same concentration at 18°."

the oxide of silicon, is the most inert and immobile of rocks ; the oxide of boron is only less available as a movable constituent of the environment; and there is no other stable compound of either element which can be compared with carbonic acid for its mobility. It must be remembered that this property is the result of two independent characteris- tics of the latter substance, its gaseous na- ture, and the precise degree of its solubility in water. Finally, the regulation of the reaction of aqueous solutions by means of carbonic acid has to be taken into account.

Hence it may be concluded that hydrogen, oxygen, and carbon, water and carbonic acid, are not to be rivaled in their own qual- ities, even as these cannot be balanced by others which they do not possess. On the whole, then, we niay believe that the physico-chemical characteristics of material systems and material processes have been com- prehensively examined in the course of the present study. Accordingly, we may finally conclude that the fitness of water, carbonic acid, and the three elements make up a unique ensemble of fitness for the organic mechanism. The search, however incomplete, has certainly not overlooked properties so important and so numerous, or compounds and elements so

With the assurance that, in such measure as the present state of science permits, our study has been indeed exhaustive, a final argument arises. So far as we can see, all the properties of water, carbonic acid, and the three elements are fit, according to our defi- nition of fitness. There is nothing about these substances that is really and seriously inferior to the same thing in any other substance; and in all the subjects which we have reviewed not a single disability of the primary constit- uents of the environment has come to light.

For the convenience of my readers the argu- ment which has been developed in the course of the preceding pages is here re-stated in outline. I. Fitness is a mutual or reciprocal relationship between the organ- ism and the environment. II. Life is a mechanism (froin the point of view of physical sci- ence) . Accordingly it must be — h. Durable, hence well regulated physico-chemically. This con- clusion applies to — c. Endowed with a metabolism. Hence there must be ex- change with the environment of —

primary constituents of the environment are necessarily and automatically formed in vast amounts by the cosmic process. V. Water, carbonic acid, and their con- stituent elements manifest great fitness for their biologi- cal r61e. a. Water possesses a great number of unique or very unusual prop- erties, e.g. thermal proper- ties, solvent power, dielectric constant, surface tension, which together result in max- imal fitness in certain respects, e.g. mobility, ubiquity, con- stancy of temperature and richness of the environment, richness of the organism in chemical constituents, variety of chemical processes, electri- cal phenomena, colloidal phe- nomena.

usual properties, e.g. mag- nitude of absorption coeflB- cient, strength as acid, which together result in maximal fit- ness in certain respects, e.g. mobility, ubiquity, richness of the environment and organ- ism in other elements and compounds, constancy of re- action, etc. carbon, hydrogen, and oxygen possess unique properties, e.g. number, variety, complexity, activity, variety of chemical relations and reactions, heats of reaction, instability, etc., which together result in maxi- mal fitness in certain respects, e.g. as sources of matter and energy for the processes of metabolism, as sources of com- plex structures, as the means of establishing complex func- tions, etc. VI. Oceans are formed automatically in

the cosmic process. VII. The ocean possesses unique properties, e.g. mobility, richness in dis- solved substances, durability, and stability of physico-chem- ical conditions, depending chiefly upon the properties of water and carbonic acid, which together result in maximal fit- ness in certain respects, e.g. as milieu, and as source of matter for the processes of metabolism, to moderate and equalize temperature, etc. VIII. The physical and chemical properties which have been taken into consideration include nearly all those which are known to