The Fitness of the Environment

AT every stage of our inquiry we have seen that the unique properties of water and carbonic acid contribute vitally important characteristics to the ocean. Such conclusions accord with the ordinary experiences of life, and they gain in significance from the un- doubted fact thj,t -organic beings first existed, ai]id_fo^r^a^.^y_Jong^Jime exi^^ onlyTiHr the waters. On this account it will be well to pause before attacking the problems of organic chemistry, and, in somewhat greater detail, to examine the ocean in its relation to the inhabitants of the globe. Thus we shall be able more clearly to perceive the manner in which, in one most important instance, the properties of water and carbonic acid operate to fit the world for life.

The most Striking of all the ocean's qualities is its constancy. No doubt since its origin it has grown colder and more saline, and has changed its reaction from faintly acid to faintly alkaline. But a million years are little in such great slow processes, and no living thing has ever experienced appreciable change in any one of them. Modern research in oceanography has de- tected surprisingly little variation in the tem- perature of the ocean. ^ The temperature of surface water depends upon the climatic character of the locality, but it is subject to far less variation than the temperature of the atmosphere above it, and is higher than the latter. The accompanying tables ^ indicate the nature of some of the variations in the temperature of sea water.

Annual Ranges of Temperatures of Ocean Water AND OF THE Am Over Land * Nearly all the facts contained in the present chapter have been drawn from the following works : S. Gunther, "Hand- buch der Geophysik " ; Arrhenius, "Kosmische Physik " ; and Hann's "Climatology," translated by Ward. According to Schott the variation of surface temperature of the open ocean over the whole globe is never less than 1° nor more than 15°. Such variations are slight on the equator, larger in the region of the trade winds, less again in the northern and southern seas.^ The surface temperature extends only a short distance into the water, thus constituting a warm surface layer. It has indeed been known since the time of Aristotle that the depths of the sea are cold. In the open ocean the temperature increases steadily as the depth increases, but more rapidly near the surface, more slowly at greater depths. The bottom water at great depth varies from a temperature of 2° in the tropics to about — 2° in the polar waters. Such low temperature of the depths of the tropical oceans is almost certainly due to the inflow of cold water from high latitudes.

In the Atlantic the temperature varies ap- proximately as follows with increasing depth : — In the Mediterranean, where no cold cur- rent flows in at the bqttom of the ocean, the temperature sinks rapidly to 11° at a short distance below the surface, and thereafter re- mains constant. This is due to the fact that in winter the surface water is cooled to that temperature and sinks, remaining then pro- tected from the summer heat by the warmer layer of less .density above.

The slight range of ocean temperatures, whether with changing seasons, with chang- ing depth, or with changing latitude, depends primarily upon the latent heat of water, especially its heat of vaporization, and upon the very high freezing point, as already ex- plained in the discussion of these physical properties. Far more constant than the temperature is the alkalinity of sea water. It has been stated above that the extreme variation in concentra-

tion of ionized hydrogen is from O.OOOOOOOllN to 0.0000000045 N. In his studies during a voyage of five months in the summer season of 1910 of the Danish steamship Thor, Palitzsch made the following observations : ^ surface water from the Skager-Rack, from the south- ern portions of the North Sea, and from the west of the Baltic ranged from about 0.000000010 N to about 0.000000009 N ; in the North Sea the surface water varied from 0.0000000083 N to 0.0000000074 N ; at the lati- tude of Murray Firth, twenty miles from the coast, the values were between 0.0000000071 N and 0.0000000066 N. In the Atlantic the surface water corresponded in the most north- ern portions to that of the North Sea, while in the Bay of Biscay and along the coast of Portugal the values were 0.0000000056 N, corresponding to slightly increased alkalinity, especially if account be taken of the rising temperature. In general the waters of the Mediterranean corresponded to those of the coast of Portugal. But from the Sea of Mar- mora, the Bosphorus, and the Black Sea samples were obtained which gave the value

1 Palitzsch, " Comptes-rendus des travaux du Laboratoire de Carlsberg," lOme Volume, p. 85, 1911. h ydrogen ion concentr ation increased, the alkalinity accordingIy~dimiriished. The only variation from the truly remark- able constancy of reaction of the ocean, so far as we know, is in the case of the Black Sea. But this sea, at depths below 180 meters, con- tains sulphurous acid, which undoubtedly accounts for the slight diminution of alkalin- ity recorded in the table. This last obser-

vation also provides a striking example of the eflSciency with which the reaction of sea water is maintained. In spite of the unusual circumstances here the variation is inconsider- able. The only known important factor which operates to establish and to preserve the re- action of sea water is the carbonate equilib- rium. There is one consideration which must be especially noted before passing on. The most obvious effect of slight changes of temperature, and of slight changes of alkalinity as well, is upon the velocity of chemical reactions. In this respect the effect of hydroxyl ions is likely to be in proportion to their concentra- tion,^ and the effect of temperature is usually such that a change of about ten degrees doubles the velocity of the reaction.^ Hence ordinary chemical reactions will progress about eight times as fast in the hottest as in the coldest ocean waters, and about seven times as fast in the most alkaline as in the least alkaline parts of the ocean. But in the case of any organism inhabiting a particular locality such changes in reaction velocity will be scarcely

* The chief actions of hydroxyl ions are catalytic, and, as in the case of the catalysis of esterification, the efEect is pro- portional to the concentration of the hydroxyl ions. appreciable. Accordingly, the regulation is physiologically adequate. The concentration of sea water is another nearly constant characteristic, though gener- ally speaking the salinity is somewhat greater on the high seas than near the coasts, where fresh water is constantly diluting the salt water, and there are some other causes which produce slight variations. The average salt content is about 3.45 per cent. The quan- tities of the rno|e~ vigiportant constituents, calculated from:- i^^^mar's data,^ are as fol- lows : —

Sodium, Na . Magnesium, Mg Calcium, Ca . Potassium, K CMorine, CI . Sulphate, SO4 Carbonate, CO3 Bromine, Br . , Most of the other numerous constituents are present in very small quantities. For in- stance, in each metric ton of sea water there 1 Dittmar, Report of Voyage of the Challenger, 1884, p. 203. The original data were calculated upon the erroneous assumption that the various salts exist in solution independ- It has been calculated that 166,000,000 years have been required for the streams to carry into the sea the sodium chloride which is now present. The calcium carbonate of the rivers would however suffice to supply the present amount of that substance in 500,- 000 years. Accordin^frai^e^present store of the latter substance re]^ ^'^nts but a very small fraction of what has passed through the ocean, and as a result of the intervention of life has finally been deposited as sedimentary limestone. Since the formation of the ocean, if present conditions correspond with the past, water must have carried to the dwellers of

ently of one another. Thus the composition of sea water is stated as follows : — the sea not less than 300,000,000,000,000,000 tons of calcium carbonate, which they have temporarily utilized as structural material. Whether this estimate be correct or not, the process is certainly the cause of the most considerable change wrought by life upon the face of the earth. The relative qiiantities of the several saline constituents of the oc ean are ^^j tardry" at a ll ^ub3ecr"t o""viTiation. Chlorine, for example, makes up never less than 55.21 per cent and never more than 55.34 per cent of all the dis- solved inorganic substances, so that the total salinity may be readily estimated with consid- erable accuracy by titration of the chlorides. Such constancy is due to the elaborate mixing of the waters resulting from ocean currents. There can be no doubt, however, that the relative amounts of the different acids and bases have slowly but steadily changed during the progress of geological evolution. Many substances, like calcium carbonate, have been steadily removed, a few, like sodium chloride, have steadily accumulated without loss.

The total salinity of the ocean, as stated above, is subject to slight variation. Along the North American coast, in the polar cur- rent, upon the coast of Norway, and toward the south of South America, the concentration of the Atlantic is 3.2 per cent to 3.3 per cent. Areas where the concentration ranges from 3.3 per cent to 3.4 per cent are still more extensive. The greater part of the North Atlantic ranges in concentration from 3.5 per cent to 3.6 per cent. In general there is a region of maximum concentration between the Equator and the Pole.

The Mediterranean, the Red Sea^ and other similar bodies of water possess a somewhat higher salt concentration, dependent upon excessive evaporation and the absence of great currents ; but only in exceptional cases and small isolated bodies of water does the concentration rise above 4.1 per cent. The salinity of ocean water varies also with the depth. In seas where there is a great influx of fresh water the surface is less con- centrated than the depths; in seas where there is much evaporation the surface is more concentrated than the depths. In the latter case the higher temperature of the surface causes expansion of the more concentrated water, and enables it to remain above. When these two influences of dilution and evapora- tion are combined, they may bring about a yearly variation of salinity. Such variations of the environment are important to animal life, slight though they may be. Thus the

herring in tlieir migrations keep to a water whose concentration ranges from 3.2 per cent to 3.3 per cent. From the constancy of the relative pro- portion of the salts in sea water it follows that every such constituent is subject to no greater variations than the sum of all. Interesting recent experiments have shown this fact to be of vital consequence to living organisms. Thus a host of experiments of Loeb and his pupils, and of others, have demonstrated re- markable toxicity in the action of pure salts, physiologically antagonistic actions of vari- ous pairs of salts, and peculiar advantages of media containing a variety of salts in definite relative amounts.^ Of all such balanced solu- tions sea water is by far the best, a condition which is almost certainly due to the processes of organic evolution. Herbst ^ has shown that the development of the fertilized eggs of sea urchins can only take place in the presence of the chlorides, sulphates, and car- bonates of sodium, potassium, calcium, and magnesium, and in a faintly alkaline reaction. Every one of these substances is essential,

* See the article by Loeb in Oppenheimer's "Handbuch der Biochemie." except that in a measure potassium may be replaced by rubidium and caesium, and chlo- rine by bromine. Moreover the relative con- centrations are of the highest importance. Thus it has become clear that the remark- able relative and absolute constancy of the chemical composition of sea water is biolog- ically far more important than formerly could be surmised. This characteristic of the ocean undoubtedly fits it for living things as they exist.

It is further to be noted that the salinity of sea water is proportional to its osmotic pres- sure. This important property also is there- fore nearly constant. When a solution is inclosed in a membrane, a bladder, for example, and the latter is im- mersed in water, both water and dissolved substance pass through the wall of the mem- brane. Ordinarily, however, the water will move much more rapidly than the dissolved- substance, hence the volume of the solution will increase, and hydrostatic pressure will be established. If a well-supported mem- brane of cupric ferrocyanide be substituted for the bladder, the process will be modified, in that water alone, not the dissolved sub- stance, can pass through the membrane, which is accordingly termed semigermeable.

Under these circumstances the pressure, called osmotic pressure by van't Hoff, may be very great. According to the theories of van't Hoff and Arrhenius this pressure is, in the case of dilute solutions, proportional to the total number of particles (molecules plus ions) which are present in solution. In its magni- tude and the laws governing its variation such pressure corresponds exactly to gaseous pres- sure. In fact the theory of solution consists primarily in the extension of the laws of Boyle cind Gay-Lussac, of the hypothesis of Avo- gadro, and of the manifold theoretical develop- ments which have been based upon them, to solutions. The great force of osmotic pres- sure always comes into action when solutions are in contact with permeable or semiper- meable membranes. It must therefore al- ways be reckoned with in physiology. The biological importance of the constancy of the osmotic pressure of sea water is strikingly exemplified by the precision with which every higher vertebrate preserves constant the os- motic pressure of its own body fluids, all at about seven or eight atmospheres.

It may readily be shown that the osmotic pressure of a solution is proportional to the depression of its freezing point, and accord- ingly osmotic pressure is commonly estimated with the help of this relationship. In the following table the facts regarding blood sera of certain animals are collected.^ In man the freezing point depression of the blood is, under ordinary circumstances, practi- cally constant, and there can be no doubt that such is the case for all highest organisms. Accordingly the differences in the above table may be taken to indicate slight constant dif- ferences between the different species.

The marine animals, except a few of the vertebrates, are adjusted in their osmotic pressures to the water which surrounds them. As in the following table so in another lo- cality where the freezing point of the water was —1.9° the body fluids of the animal were again found to agree with it. It is therefore evident that constancy of osmotic 1 Hober, "Physikalische Chemie der Zelle und der Gewebe." The great importance of osmotic pressure is also attested by many of the facts of phys- iology. The study of this subject has in- deed from its origin always been .closely associated with the biological sciences, and it was in great part biological experiments and wholly experiments of biologists which were employed by van't Hofif in his development, on the basis of osmotic phenomena, of the theory and laws of dilute solutions.

Absorption, secretion, excretion, and the movement of substances across membranes. — to say nothing of the establishment of liquid currents within the body, — are all related to osmotic pressure. The forces in- volved in such processes are large, and osmotic phenomena assume a special importance wherever colloidal systems occur. It appears to be certain that osmotic pressure is now se- curely established as one of the fundamental factors in the physico-chemical organization of the living mechanism, and one of the constant conditions, like concentration of the several constituents, alkalinity, temperature, etc., whose preservation is of vital importance.

There are a number of causes which bring about ocean currents. In the tropics high temperature causes a far greater evaporation of water than can be oflfset by rainfall and the flow of rivers ; near the poles this relation is reversed. Hence water must steadily flow from high to low latitudes, there to evaporate and complete the cycle in the atmosphere and on the land. In polar regions the cold water sinks and penetrates along the bottom of the sea in great deep currents to the tropics.

The surface currents of the ocean have a different origin, for they depend upon winds, especially trade winds, etc. Such continuous action of moving air upon water has been theoretically explained by Helmholtz and Zopperitz. Needless to say, in addition to these principal causes there are a great variety of lesser factors which assist in the formation and preservation of ocean currents. It is impossible here to undertake an analy- sis of the phenomenon, but certain it is that into the processes that constantly stir the ocean, beside the rotation of the earth, the eccentricity of its orbit, and the inclination of its axis, the thermal properties of water enter as fundamentally important factors.

The magnitude and the extent of the movements which result from such influences are very considerable. The principal surface currents are oval in form, one in the North Pacific between 10° and 50° north latitude, one in the North Atlantic between 10° and 30° north latitude, one in the South Pacific between 5° and 45° south latitude, one in the South Atlantic between 0° and 40° south latitude, and one in the Indian Ocean between 0° and 40° south latitude. The greatest of these are the Pacific currents. In the far south is an Antarctic current flowing from

west to east; in the north a current flows from east to west, from the Siberian coast to Northeast Greenland and thence along the east coast; another flows from Baffin's Bay along the east coast of North America. Of all ocean currents, the Gulf Stream, a branch of the northern equatorial current, has been most carefully studied. Its maxi- mum velocity is 220 kilometers per day, greater therefore than that of the Rhine at Coblentz ; the mean about 134 kilometers a day. In the Straits of Yucatan the Gulf Stream carries 0.2 cubic kilometer (200,000,- 000 tons) per second. If all this water were to be cooled to the temperature of the polar ocean this would be equivalent to the trans- port of about 5,000,000,000,000,000 gram calories per second. The magnitude of this quantity, of course, depends upon the specific heat of water.

In this manner vast quantities of water, carrying enormous stores of heat, are constantly in motion all over the globe. The result is> that homogeneity of the ocean which has beerl discussed above, — constancy of concentra- tion, of composition, of temperature, of alka- linity, and of osmotic pressure. There are, in accordance with our funda- mental postulates of the characteristics of life, two principal requirements of the living organism which an environment must ful- fill, — such a supply of matter and energy for food as may be suitable to a complex mechanism, and stability of conditions.

After a general review of the chief character- istics of the ocean, it is therefore necessary to examine them more particularly in relation to such requirements. In so doing it must not be forgotten, however, that these characteristics of the ocean which we have just discussed are only in part due to the unique physical proper- ties of water which have been already dis- cussed in Chapter III, and to those of carbonic acid which have been discussed in Chapter IV. In part they depend upon the mere magnitude of the sea, on the stability of the solar system and the consequent antiquity of the geological and meteorological processes, and upon a great variety of astronomical and geophysical conditions. However, we shall only a little extend the scope of our inquiry if we now consider water not only as an indi-

vidual chemical substance, that is to say ab- stractly, but also naturally, as automatic processes of cosmic and geological evolution have fashioned it into the principal constit- uent of the face of the globe. Primarily, at any rate, the outcome of such processes is dependent upon the inherent properties of water and upon the quantity of it which is present on the surface of the earth, and the subject is too important to be passed com- pletely by.

Perhaps the first desideratum in an en- vironment as a source of food is mobility. Any organism which, like the lilies of the field, need not toil for its nourishment, is in most favorable conditions, and such conditions are the principal cause of the enormous wealth of vegetation upon the earth. Now the ocean, apart from the flora and fauna which inhabit it, is perfectly homogeneous ; hence its mobility brings to an organism all that it has to offer, and even sweeps along organic nourishment as well. In the ocean not only plants but many animals may remain motionless and, like the oyster, await the food that will surely be borne to them; or they may float freely, relying on the mixing of the water to bring them into contact with their food.

environment are important. It is certainly impossible to imagine a medium more rich and varied in elementary constituents than sea water, unless it be sea water with still other sub- stances added to it. But, in the first place, there are few absent elements which might be added, and, in the second place, the addition of other substances would be likely to cause the escape of bodies which are present. At all events, the ocean is certainly more favor- able in these three respects than if it were anything else that could occur in the course of nature. Almost ideally mobile, rich, and varied, the sea is an almost perfect source of supply for a complex mechanism. To be sure there are great difficulties in extracting its constituents from sea water, and the efficiency of physiological processes is a factor essential to their utilization, but at least there stand materials ready for the mechanism which can employ them.

The predominance of water, no doubt, forces that substance upon living beings as their chief constituent; in view of the fitness of water for the purpose that is in itself a favor- able circumstance. Otherwise the organism is left free to choose from all the common elements, and from some of the rare ones, what may be most suitable to its purposes at every stage of the infinitely varied process of organic evolution. As a result we find here and there in the marine flora and fauna almost every element which the sea affords concentrated and put to use.