The Wonders of Life: A Popular Study of Biological Philosophy. Ernst Haeckel
Читать онлайн книгу.
understood the chemistry of the compounds of carbon, that element being distinguished from all the others (some seventy-eight in number) by very important properties. It has, in the first place, the property of entering into an immense variety of combinations with other elements, and especially of uniting with oxygen, hydrogen, nitrogen, and sulphur to form the most complicated albuminoids (see the Riddle, chapter xiv.). Carbon is a biogenetic element of the first importance, as I explained in my carbon-theory in 1866. It might even be called "the creator of the organic world." At first these organogenetic compounds do not appear in the organism in organized form—that is to say, they are not yet distributed into organs with definite purposes. Such organization is a result, not the cause, of the life-process.
I have already shown in the fourteenth chapter of the Riddle(and at greater length in the fifteenth chapter of my History of Creation) that the belief in the essential unity of nature, or the monism of the cosmos, is of the greatest importance for our whole system. I gave a very thorough justification of this cosmic monism in 1866. In the fifth chapter of the Generelle Morphologie I considered the relation of the organic to the inorganic in every respect, pointing out the differences between them on the one hand, and their points of agreement in matter, form, and force on the other. Nägeli some time afterwards declared similarly for the unity of nature in his able Mechanisch-physiologische Begründung der Abstammungslehre(1884). Wilhelm Ostwald has recently done the same, from the monistic point of view of his system of energy, in his Naturphilosophie, especially in the sixteenth chapter. Without being acquainted with my earlier work, he has impartially compared the physico-chemical processes in the organic and inorganic worlds, partly adducing the same illustrations from the instructive field of crystallization. He came to the same monistic conclusions that I reached thirty-six years ago. As most biologists continue to ignore them, and as, especially, modern vitalism thrusts these inconvenient facts out of sight, I will give a brief summary once more of the chief points as regards the matter, form, and forces of bodies.
Chemical analysis shows that there are no elements present in organisms that are not found in inorganic bodies. The number of elements that cannot be further analyzed is now put at seventy-eight; but of these only the five organogenetic elements already mentioned which combine to form plasm—carbon, oxygen, hydrogen, nitrogen, and sulphur—are found invariably in living things. With these are generally (but not always) associated five other elements—phosphor, potassium, calcium, magnesium, and iron. Other elements may also be found in organisms; but there is not a single biological element that is not also found in the inorganic world. Hence the distinctive features which separate the one from the other can be sought only in some special form of combination of the elements. And it is carbon especially, the chief organic element, that by its peculiar affinity enters into the most diverse and complicated combinations with other elements, and produces the most important of all substances, the albuminoids, at the head of which is the living plasm (cf. chapter vi.).
An indispensable condition of the circulation of matter (metabolism) which we call life is the physical process of osmosis, which is connected with the variations in the quantity of water in the living substance and its power of diffusion. The plasm, which is of a spongy or viscous consistency, can take in dissolved matter from without (endosmosis) and eject matter from within (exosmosis). This absorptive property (or "imbibition-energy") of the plasm is connected with the colloidal character of the albuminoids. As Graham has shown, we may divide all soluble substances into two groups in respect of their diosmosis—crystalloids and colloids. Crystalloids (such as soluble salt and sugar) pass more easily into water through a porous wall than colloids (such as albumen, glue, gum, caramel). Hence we can easily separate by dialysis two bodies of different groups which are mixed in a solution. For this we need a flat bottle with side walls of india-rubber and bottom of parchment. If we let this vessel float in a large one containing plenty of water, and pour a mixture of dissolved gum and sugar into the inner vessel, after a time nearly all the sugar passes through the parchment into the water, and an almost pure solution of gum remains in the bottle. This process of diffusion, or osmosis, plays a most important part in the life of all organisms; but it is by no means peculiar to the living substance, any more than the absorptive or viscous condition is. We may even have one and the same substance—either organic or inorganic—in both conditions, as crystal or as colloid. Albumen, which usually seems to be colloidal, forms hexagonal crystals in many plant-cells (for instance, in the aleuron-granules of the endosperm), and tetrahedric hœmoglobin-crystals in many animal-cells (as in the blood corpuscles of mammals). These albuminoid crystals are distinguished by their capacity for absorbing a considerable quantity of water without losing their shape. On the other hand, mineral silicon, which appears as quartz in an immense variety (more than one hundred and sixty) of crystalline forms, is capable in certain circumstances (as metasilicon) of becoming colloidal and forming jelly-like masses of glue. This fact is the more interesting because silicium behaves in other ways very like carbon, is quadrivalent like it, and forms very similar combinations. Amorphous (or non-crystalline) silicium (a brown powder) stands in relation to the black metallic silicon-crystals just as amorphous carbon does to graphite-crystals. There are other substances that may be either crystalloid or colloid in different circumstances. Hence, however important colloidal structure may be for the plasm and its metabolism, it can by no means be advanced as a distinctive feature of living matter.
Nor is it possible to assign an absolute distinction between the organic and the inorganic in respect of morphology any more than of chemistry. The instructive monera once more form a connecting bridge between the two realms. This is true both of the internal structure and the outward form of both classes of bodies—of their individuality (chapter vii.) and their type (chapter viii.). Inorganic crystals correspond morphologically to the simplest (unnucleated) forms of the organic cells. It is true that the great majority of organisms seem to be conspicuously different from inorganic bodies by the mere fact that they are made up of many different parts which they use as organs for definite purposes of life. But in the case of the monera there is no such organization. In the simplest cases (chromacea, bacteria) they are structureless, globular, discoid, or rod-shaped plasmic individuals, which accomplish their peculiar vital function (simple growth and subdivision) solely by means of their chemical constitution, or their invisible molecular structure.
The comparison of cells with crystals was made in 1838 by the founders of the cell-theory, Schleiden and Schwann. It has been much criticised by recent cytologists, and does not hold in all respects. Still it is of importance, as the crystal is the most perfect form of inorganic individuality, has a definite internal structure and outward form, and obtains these by a regular growth. The external form of crystals is prismatic, and bounded by straight surfaces which cut each other at certain angles. But the same form is seen in the skeletons of many of the protists, especially the flinty shells of the diatomes and radiolaria; their silicious coverings lend themselves to mathematical determination just as well as the inorganic crystals. Midway between the organic plasma-products and inorganic crystals we have the bio-crystals, which are formed by the united plastic action of the plasm and the mineral matter—for instance, the crystalline flint and chalk skeletons of many of the sponges, corals, etc. Further, by the orderly association of a number of crystals we get compound crystal groups, which may be compared to the communities of protists—for instance, the branching ice-flowers and ice-trees on the frozen window. To this regular external form of the crystal corresponds a definite internal structure which shows itself in their cleavage, their stratified build, their polar axes, etc.
If we do not restrict the term "life" to organisms properly so-called, and take it only as a function of plasm, we may speak in a broader sense of the life of crystals. This is seen especially in their growth, the phenomenon which Baer regarded as the chief character of all individual development. When a crystal is formed in a matrix, this is done by attracting homogeneous particles. When two different substances, A and B, are dissolved in a mixed and saturated solution, and a crystal of A is put in the mixture, only A is crystallized out of it, not B; on the other hand, if a crystal of B is put in, A remains in solution and B alone assumes the solid crystalline form. We may, in a certain sense, call this choice assimilation. In many crystals we can detect internally an interaction of their parts. When we cut off an angle in a forming crystal, the opposite angle is only imperfectly formed. A more important difference between the growth of crystals and monera is that