Elements of Physical Biology

Chemical Correlation in Soil and in Organism. Our ancestral resemblance to the soil from which we spring is also exhibited by evidence converging from a different source. H. S. Washington, 19 This observation must be accepted with some caution. Compare Whitney, Science, 1922, vol. 56, p. 218. “Until we determine the actual loss, through chemical denudation, of silica, alumina, iron, potash and other electrolytes in the colloidal state, carried by rivers, we are in no position to even speculate as to whether erosion is a selective process which might change the chemical composition of the soil.”

in his studies on The Chemistry of the Earth’s Crust, already cited, draws attention to the fact that in the rocks soda and iron tend to be associated together as a pair on the one hand, and potash and magnesia on the other. This is well brought out in the diagram figure 44, reproduced from Washington’s memoir, in which it is seen that the points representing the analysis of a number of rock samples tend to group themselves about the diagonal of the square, indicating that

Fig. 44. CorRELATION IN THE OccURRENCE OF Na, Fe anp K, Mg 1N Rocks A large number of analyses here plotted show a marked tendency to array themselves along the diagonal, showing that high percentage of Na is commonly associated with high percentage of Fe; K and Mg follow a similar relation. After H. 8. Washington. high content of soda goes together with high content of iron, but with low potash and low magnesia; and vice versa. The point of special interest to us here in the present connection is that to which Dr. Washington draws attention in the words:

Curiously enough, the same correlation between these two pairs of elements, soda and iron, and potassium and magnesium, seems to hold good in the organic world. This is apparently shown by the following facts: In autotrophic plant metabolism potash is an essential element, as is also magnesium, in that chlorophyll (which in the leaves acts as the carbon-transferring substance) is a magnesium salt of a complex organic acid, while sodium and iron are generally toxic toward (at least the higher, gymnospermous and angiospermous) plants. On the other hand, sodium, rather than potassium, is the alkali metal essential to the higher animals, salt being a very necessary article of diet (in part because of its chlorine, and in part because of its sodium, content), and sodium chloride is present in the blood plasma; and at the same time, hemoglobin and its derivatives (which act as oxygen carriers, and are analogous to chlorophyll in plants) are iron salts of organic acids closely related to that of chlorophyll; while, similarly potassium and magnesium are more toxic toward the higher animals than are the other pair.

This singular parallel must not, of course, be looked upon as an instance of resemblance due to anything of the nature of inheritance of ancestral traits in the biological sense. Rather must it be connected in our minds with the fact that systems composed of the same fundamental substances, will display certain analogies through interplay, in them, of the same chemical affinities. Accessibility of Valuable Earth-Constituents. Such a comparison as has been made above of the relative abundance of the several elements in the living organism and in the environment from which it draws its supplies, would be misleading if attention were not drawn to another factor aside from abundance, which enters strongly into play in the quest for the necessities of life. More important than mere abundance is accessibility. For, a substance may be present in comparatively large quantities, and yet be difficult to lay hold of, either on account of its wide dispersal in dilute form, or for other reasons. On the contrary, a comparatively rare substance may be procurable with relative ease, if it occurs segregated in concentrated or otherwise readily accessible form. Perhaps the most telling illustrations of this are to be found in industry. The element copper for

example is found only to the extent of about 1000 P& cent in the earth’s crust. Yet it is one of the most important metals in the arts, and is not ordinarily thought of as particularly rare. This is because, in those regions where it does occur, it is found in concentrated form, either as native metal, or as rich ore. Other instances are readily cited. Tin, lead and zine are all rarer than copper, and each rarer than its precursor, in the order named. Still rarer are silver, tungsten, gold, bromine and platinum, all of which find important use in

DVZOIZ GHL TAOMY ‘SLNGWAIY OINGDOULAY OLN NOISIAI(] DNIMOHY ‘SLNEWGTY GHL dO NOILVOIMISSVIO oladorumg “Cp ‘DIY the arts. But the mode of occurrence of these substances is such that they can be gathered or mined with comparative ease. It has been pointed out by H. S. Washington that the elements, as arranged in Mendeleeff’s table, naturally fall into two groups divided by a zigzag line, as shown in figure 45. Above this line are the rock elements or petrogenic elements, that enter into the principal rock-forming minerals (and also, the gases of the atmosphere). Below the line are the ore elements or metallogenic elements, which commonly occur in concentrated form as ores and as native metal.

Now man’s industrial activities are merely a highly specialized and greatly developed form of the general biological struggle for existence; and this same feature of accessibility and of concentration in segregated supplies (ores and the like), which is a prime condition for the very existence of some of our industries, is also involved, in closely analogous manner, in the more primitive life processes. Our fields demand fertilizers bringing ammonia, nitrates, potash, phosphates, etc., in suitably concentrated form, if they are to bear a harvest commensurate with the needs of a modern community. And this again is merely an accentuated example of the still more primitive needs of the unsophisticated flora and fauna of virgin nature. Of scattering, dissipating processes there are plenty. Rain and snow wash most of what is soluble, and much that is not, into the rivers and out to sea. Our own activities in modern intensive agriculture bring each year to the land a highly concentrated diet of fertilizers, which in the very act of cultivation are scattered and diluted many thousand times. And our modern sewage system is deliberately wasteful of vital substances, which it discharges into streams and out to sea. All this dissipation must in some way be balanced if the régime is to continue. Thus the circulation of matter in nature must not only provide for the mere presence of certain substances on which the maintenance of life depends, but it must furnish them in suitable concentration and, generally, in available form. It must, therefore, in many cases include, as a definite step, a segregating or concentrating process”? as well as simple motion through a cycle.

We shall have occasion to note concrete illustrations of this in the separate consideration of the circulation of the several elements, to which we now proceed. 20 The significance of this from the point of view of energetics will engage our special consideration in a later section. The great Sea-water finds its way Through long, long windings of the hills; And drinks up all the pretty rills Then hurries back the road it came— Returns on errand still the same; This did it when the earth was new; And this for evermore will do As long as earth shall last. —Wordsworth.

The ancients, totally blind as they were perforce to the fine details of material transformations revealed by the search light of modern chemistry, nevertheless recognized in its broad features the cycle of life, the circulation of the elements in nature. “Dust thou art, and unto dust shalt thou return,” we read in an old book of wisdom. Heracleitus (536 to 470 B.C.), promulgator of the famous doctrine nrayra pet has a more detailed, if not more accurate conception of the cycle of Nature, which he formulates in these terms:

The human mind was not yet schooled, then, to polish the facets of this rough gem, and bring out the sharp-edged truth as we see it today But all honor to the minds that discerned through the mists of dawn the bold features of the landscape to be revealed in the sunlight of later day. Today we recognize not four elements, but over ninety, not counting those modern variants, the isotopes. And we follow in much detail not one cycle, but, as particularly pertinent to life, five major cycles—the circulation of water, carbon, oxygen, nitrogen and phosphorus. This was noted already at the conclusion of Chapter XIV, but the discussion of the cycles was deferred to give space to a preliminary survey of the scene in which these cycles churn the planet’s surface in their age-long duty.

We are now prepared to take up the thread where we broke off; we turn our attention first to the water cycle. Water Requirements of Human Body. We do not ordinarily class water as a food, though we partake of it by the same channel that gives entrance to the materials commonly so classed, and although the lack of water, if we are by any circumstance deprived of this substance, is felt even more acutely than an interruption in the adequate supply of food. The fundamental basis for this distinction, its origin in the unsophisticated mind, isundoubtedly the fact that we have a separate sense of thirst, distinct from the signals of hunger and appetite originating from nutritive demands of the body. And this naive, unsophisticated distinction is entirely in accord with the reasoned analysis of the respective functions of water and of food in the narrower sense. It is undoubtedly just because of this difference in function that thirst and hunger have been developed as separately recognized sensations. Water acts merely as a vehicle ; unlike the food, which undergoes extensive and complicated reactions within the economy, water leaves the body essentially as it enters it, unchanged chemically, though charged (in part) with substances in solution.

It would be a gross error, however, to suppose that water, because it functions thus in accessory capacity, and escapes the more intimate transmutations of metabolism, can be lightly regarded in making a survey of the participation of the several elements in the cycle of nature. It must be remembered that water constitutes as much as 60 per cent of the total mass of the human body, for example, and a still greater proportion of the substance of most of our food-stuffs, as shown in table 20,

Thus an adult human being consumes per diem about 3 liters of water of which about 1 liter is contained in his solid food. In point of fact he consumes about 5 pounds of water for every pound of dry solid matter ingested. It is thus seen what an important item water is in the daily economy of the human organism. The excretion of water by the kidneys, lungs, intestine and skin is somewhat in excess of the intake. The excess of the outgo over the intake is formed in the body by the oxidation of hydrogen organically combined.

Water Requirements of Plants. Rainfall as a Limiting Factor. In the economy of most plants the traffic of water is of even greater importance? than in man and land animals generally, and Mesriresh ass astro: leon 43-65 | Sugar granulated............ 0 LIEV 9 aie. See Ae SR ADT lie Cabbbagey eins. cee oct cceit 78 CIA), once Cee) Oa ae PR 66 Ciucwmbersa: cessor. on 81 (BATA ee ie a ee 11 POPALOEB Ss. Wt Rea icees ce nee 63 Vigil aes Fig ra Wi Raha eae ee 87 AP OMA MEORA cis, ous ieee cisions SEI 94 Cheese, Cheddar. ........:.:.: 27 UL AWDEMTIEG silks «2 aeGidehaslel 86 Nikeag fours: 5. eee esa 12 Walnut, California.......... 1 MMiho ye CHitey so taees hats oie el: 35

indirectly the moisture needs of plants are, of course, of fundamental importance also to the animal population feeding on the vegetable growth of the soil, so that the water supply of a territory 11. J. Henderson (The Fitness of the Environment, p. 133) estimates that a man weighing 60-70 kgm. excretes daily: grams TEL ef een UN Noe Dis Veh ab acspat cela eld ode aya alle 01 8b. 0: SI Pe As ge 2500-3500 AUS INALCUS ACL eetereretrtete ste nits Bee a a atein diel op giere'eits a wie alow § 750-— 900 UN axdareretsqhio qichiV ete fs git orn Oy one eae Ri oo aaa Re a ca 60— 125

21. J. Henderson, loc. cit., estimates that of the materials ingested by ordinary green plants, more than nine-tenths is water, and carbon dioxide at least five sixteenths of the remaining tenth. may function as the basic limiting factor of the total life which that territory is able to support. A study of these relations with particular reference to the human population of the United States, has been made by W. J. McGee, who remarks :3 Hellriegel in Germany and King in this country have shown that crop plants require for their growth a quantity of water, measured by transpiration, averaging from 300 to 600 (with a mean of about 450) times the weight of the plants after drying; and common field experience indicates that, in addition to the moisture passing through the plants, the soil requires an even larger quantity to maintain a texture suitable for crop growth—much of which passes away through evaporation and seepage. On this basis “the agricultural duty of water’’ in this country has been formulated as the production of one-thousandth part of its weight in average plant crop. Reckoning human food and drink on this basis, and assuming that meats require (chiefly in the growth of plants used as feed for the animals) ten times the quantity of water represented in vegetal food, it appears that the adult who eats 200 pounds each of bread and beef in a year consumes something like 1 ton of water in drink and the equivalents of 400 tons in bread and 4000 tons in meat, or 4401 tons in all—figures corresponding fairly with the results of intensive agriculture in arid districts. Accordingly, the ‘‘duty of water’’ considered in relation to human population may be stated roughly as the maintenance of a human life a year for each 5 acre-feet used effectively in agriculture.

Now mainland United States (i.e., the chief body of our territory, exclusive of Alaska and the insular possessions) comprises something over 3,000,000 square miles, or somewhat less than 2,000,000,000 acres of land; yet the annual rainfall—the sole original source of fresh water—averages barely 23 feet (30 inches), or hardly 5,000,000,000 acre-feet. So while the land area, if peopled to the density of Belgium (over 640 per square mile,) would carry a population of 2,000,000,000, the water supply suffices for only 1,000,000,000.

The conclusions of McGee may have to be modified in point of detail, and some of his figures may perhaps have to be revised; but the general principle underlying his reflections attract our attention. The moisture needs of the living population (all species included) are a large and fundamental item in biological economy; whether this item proves the ultimate limiting factor of population growth, as McGee suggests, is a question whose answer must be sought in

terms of Liebig’s Law of the Minimum; a dearth of other essentials may make itself felt before the limit of available moisture is reached. The Sources of Supply. Such, then, in broad outline, are the moisture needs of organic nature; as such they have existed, in greater or less degree, for millions of years, and have been satisfied, and will continue long to be satisfied, from a source essentially inexhaustible because constantly replenished by the return flow: The great reservoir is the ocean, with its 302 million cubic miles of water, and an evaporating surface of over 144 million square miles. Annually there rise from this into the atmosphere about 63,300 cubic miles of water, to which some 22,800 more are added by evaporation from the land, making a total of 86,100 cubic miles. This figure also represents the total precipitation in rain, snow, etc., but of the total about 56,700 fall back directly into the ocean, and only the balance, 29,400 is available for the needs of the land. It has been noted that the evaporation from the land is about 22,800 cubic miles. ‘The difference between this and the precipitation on land, the balance of 6500 cubic miles, is the drainage from the land to the ocean by rivers.

No attempt will be made to estimate what proportion of the precipitation on land is derived from evaporation over the sea, and what proportion comes from the land itself. Some idea of the relation, however, can be formed from a consideration of the difference or the ratio of the rainfall within the area drained by rivers and the amount actually discharged by them into the sea. John Murray* has collected information on this subject, with the result shown in table 21, which covers 33 of the world’s principal rivers. It will be seen that the total rainfall in the area of these rivers is 10,186 cubic miles, the discharge to the sea is 2182 cubic miles, leaving a difference of 8004 cubic miles unaccounted for. A certain portion of this perhaps represents seepage, but the bulk must correspond to water reevaporated from the land and from inland waters. It will be observed that for the 33 rivers combined the proportion of the discharge to sea to the total rainfall is about one-fifth. For individual rivers the ratio varies widely, between the extreme of 0.58 (Rhone) and 0.027 (Nile). Naturally the climate very materially affects this

There is also a circulation of waters of the sea in very large di- According to L. J. Henderson’ the Gulf Stream in the Straits of Yucatan carries 200 million tons per second,® travelling Showing the drainage area, annual rainfall, annual discharge, and ratio of discharge to rainfall, of 33 rivers in different parts of the world ormovimor| —niven peeve perenne ec ree Wo square miles cubic miles cubic miles with a mean velocity of about 80 miles per day. This circulation in the ocean has of course no direct part in the water cycle of the organic world, but indirectly is most important on account of its climatic effects.

Fig. 46. CrrcuLaTION oF THE ELEMENTS IN NATURE. Tup WatER CycL5 Water Cycle Diagram. The principal figures relating to the circulation of water on the globe are exhibited in diagrammatic form in figure 46, which tells the story more effectively than words. It may here be added in explanation that the 3000 cubic miles of moisture contained in the air are practically restricted to the lower 6 miles or so of the atmosphere. For the rest, this moisture is unevenly distributed, as everybody knows from personal weather observation. Water vapor and condensed water differs in this respect from the other permanently, gaseous constituents of the atmosphere. (See table 12 and figures 40, 41.)

Fraction of Total Water Circulation Taking Part in Life Cycie. Only a fraction of the total circulation of water actually passes through the organic cycle. We may make an attempt as follows to obtain a rough idea of the order of magnitude of the fraction thus concerned. If the entire land surface were cultivated to produce crops at the rate adopted as standard by W. J. McGee, the growth produced (figured in dry weight) would be ;¢oy of the rainfall. Furthermore, this growth would evaporate, by transpiration, about 500 times its own weight of water, (this is assuming one crop per year). It would therefore evaporate just about one-half the annual rainfall. But the

total evaporation on the land is oD = three fourths of the annual rainfall on land, the remaining fourth being drained to sea by rivers. Hence, of the water evaporated on land, one-half times four-thirds = two-thirds is evaporated by plants and thus takes direct part in the organic cycle. In comparison with the evaporation by plants, that from animals is undoubtedly negligible, especially in view of the coarseness of our data. If we put the evaporation on land as one-fourth of the total evaporation, we finally arrive at the value one-sixth as that fraction of the total water in circulation, which takes actual part in the organic circulation.

Desert areas cannot materially alter this estimate, since they contribute but little to either side of the account, both evaporation and life being meagre or absent. In some measure this remark also applies to frigid wastes of the polar regions, where the low temperature makes for comparatively low evaporation (a factor counter-balanced, it is true, in some degree, by the extensive cover of ice and snow). Tor temperate zones McGee’s figure for cultivated fields is undoubtedly too high to apply as an average for the entire land. In the tropics, on the other hand, it is perhaps not excessive. On the whole the fraction one-sixth computed as above is probably too high, but perhaps it serves to give us an idea of the order of magnitude involved.

Another estimate leading to a materially lower result, is obtained as follows: If we accept Engler’s estimate that one-fiftieth of the atmospheric carbon dioxide, that is to say, 4.4 10!° metric tons, takes part in the organic cycle; and we adopt the figure given by L. J. Henderson? that the water taken up by plants, isabout 11 times the CO: which they absorb, we obtain, as a very rough estimate of the water engaged in the organic cycle, an amount of 5 X 10" metric tons, or, in round numbers, 120 cubic miles. This, then, is about 74> of the total annual circulation of water, or about $5 of the total rainfall on land.

Behold how great a matter a little fire kindleth.—St. James. If the lamp of life is a poetic symbol, it is an image essentially true to fact. Not only is life, in particular animal life, largely a combustion process: like the flame, life reaches out for fuel, and with the power gained, strains again for more. Like the flame it consumes, and it spreads. And as the fire sends out sparks, of which many die, but a few, falling upon favorable ground, flare up as a second generation, in reproduction of the parent flame; so the living creature scatters its seed, some to die, but some also to live again the life of the parent. ‘‘But,’’ someone perhaps will remark, ‘‘a fire may start without preéxisting flame; whereas all life is itself begotten of life.’”’ Is this distinction really so fundamental? In nature undisturbed by man the starting of a fire spontaneously is a rare event; and that, after all, is the most that we can say positively regarding the origination of life from the non-living—it is either so rare or so unobtrusive! an event as to have escaped our observation. No doubt it took man many thousands of years to acquire the art of lighting a fire, may not in the lapse of time a second Prometheus arise to teach us also how to kindle the torch of life? Let us not delay his coming by closing our minds to the possibility.?

‘ Compare F. J. Allen’s view, as presented by L. L. Woodruff in The Evolution of the Earth and its Inhabitants, 1919, p. 102: “Life at this stage was of the humblest kind, since there were no definite organisms, only diffuse substances trading in energy, and between this stage and the evolution of cellular organisms an immense period elapsed.’’ If this picture of the beginning of life is true to fact, the process was unobtrusive; probably, if we were shown a specimen of such elementary “living”? matter, we should not recognize it as such. All this is in accord with what has been said in an earlier chapter regarding the definition of life. If we continue to use the word life, this is merely a matter of convenience and does not imply any

departure from the point of view set forth in the opening chapters. See also p. 19. Be that as it may, the fundamental fact remains that slow combustion, oxidation as the chemist calls it, is a dominant feature in the physiology of animal life, and that the leading réles in this action are played by the elements carbon and oxygen. In our method of securing our supply of these elements there is a certain dyssymmetry. Carbon we eat in our meals; oxygen we breathe in in respiration. But in function the two elements stand in essentially symmetrical relation; the two together and impartially furnish us with the requisite energy for our life activities. Thus we must regard oxygen as food as much as carbon. This fact deserves a passing note, since it is sometimes stated that assimilation of inorganic food is a characteristic of plants, as distinguished from animals. The statement rests on an arbitrary and wholly gratuitous exclusion of oxygen from our list of foods. It just so happens that there is one item on the animal’s menu, namely, oxygen that is gaseous and is spread broadcast; does not therefore have to be hunted and captured. Toward this the animal assumes the same attitude which, presumably, plants adopt toward all their foods: he takes it in unconsiously. This touch of plant nature which we recognize in ourselves should serve to give us a sympathetic insight into the “psychology” of plants. At the same time it reminds us once again of the esentially arbitrary character of the division of organisms into two classes, animals and plants. One and the same organism possesses both animal and plant characteristies, and this is true even of that most highly specialized of all animals, the human being. In view of the symmetry in function that exists between carbon and oxygen, and the inseparable relation