The reaction from the one-sided mechanical theories shows itself in many different ways and degrees. It may, according to the individual naturalist, affect the theory as a whole, or only certain parts of it, or only particular lines. It starts with mere criticism and with objections, which go no further than saying that "in the meantime" we are still far from having reached a physico-chemical solution of the riddle of life; it may ascend through all stages up to an absolute rejection of the theory as an idiosyncrasy of the time which impedes the progress of investigation, and as an uncritical prejudice of the schools. It may remain at the level of mere protest, and content itself with demonstrating the insufficiency of the mechanical explanation, without attempting to formulate any independent theory for the domain of the vital; or it may construct a specifically biological theory, claiming independence amid other disciplines, and basing this claim on the autonomy of vital processes; or it may widen out deliberately into metaphysical study and speculation.

Taken at all these levels it presents such a complete section of the trend of modern ideas and problems that it would be an attractive study even apart from the special interest which attaches to it from the point of view of religious and idealistic conceptions of the universe.

Both Liebig and Johannes Muller remained vitalists, notwithstanding the discovery of the synthesis of urea and the increasing number of organic compounds which were built up artificially by purely chemical methods. It was only about the middle of the last century that the younger generation, under the leadership, in Germany, of Du Bois-Reymond in particular, went over decidedly to the mechanistic side, and carried the doctrines of the school to ever fresh victories. But opposition was not lacking from the outset, though it was restrained and cautious.

Virchow's "Caution".

Here, as also in regard to "Darwinism," which was advanced about the same time, the typical advocate of "caution" was Rudolf Virchow. His doubts and reservations found utterance very soon after the theory itself had been promulgated. In his "Cellular Pathologie,"(76) and in an essay on "The Old Vitalism and the New,"(77) he puts in a word for a _vis vitalis_. The old vitalism, he declared, had been false because it a.s.sumed, not a _vis_, but a _spiritus vitalis_. The substances in animate and in inanimate bodies have undoubtedly absolutely the same properties. Nevertheless, "we must at once rid ourselves of the scientific prudery of regarding the processes of life solely as the mechanical result of the molecular forces inherent in their const.i.tuent bodily parts." The essential feature of life is a derived and communicated force _additional_ to the molecular forces.

Whence it comes we are not told. He glided all round the problem with plat.i.tudinarian expressions, which were intended to show his own adherence as a matter of course to the new biological school, and which revealed at the same time his striking incapacity for defining a problem with any precision. At a "certain period in the evolution of the earth" this force arose, as the ordinary mechanical movements "swung over" into the vital.

But it is thus a special form of movement, which detaches itself from the great constants of general movement, and runs its course alongside of, and in constant relation to, these. (Did ever vitalist a.s.sert more?) After thus preparing the way for a return of the veering process at a particular stage of evolution, and giving the necessary a.s.surances against the "diametrically opposed dualistic position," Virchow employs almost all the arguments against the mechanical theory which vitalists have ever brought forward. Even the catalytic properties of ferments are above the "ordinary" physical and chemical forces. The movement of crystallisation, too, cannot be compared with the vital movement. For vital force is not immanent in matter, but is always the product of previous life.(78) In the simplest processes of growth and nutrition the _vis vitalis_ plays its vital _role_. This is true in a much greater degree of the processes of development and morphogenesis. In the phenomena of irritability life reveals its spontaneity through "responses," and so on. "Peu d'anatomie pathologique eloigne du vitalisme, beaucoup d'anatomie pathologique y ramene."

It is impossible to make much of this position. It leaves the theory with one of the opposing parties, the practice with the other, and the problem just where it was before.

Preyer's Position.

Along with Virchow, we must name another of the older generation, the physiologist William Preyer, who combated "vitalism," "dualism," and "mechanism" with equal vehemence, and issued a manifesto, already somewhat solemn and official, against "vital force." And yet he must undoubtedly be regarded as a vitalist by mechanists and vitalists alike.(79) He is more definite than Virchow, for he does not content himself with general statements as to the "origin" of vital force, and of the "swinging over"

of the merely mechanical energies into the domain of the vital, but holds decidedly to the proposition _omne vivum e vivo_. He therefore maintains that life has always existed in the cosmos, and entirely rejects spontaneous generation.

The fallacy, he says, of the mechanistic claims was due to the increasing number of physical explanations of isolated vital phenomena, and of imitations of the chemical products of organic metabolism. A wrong conclusion was drawn from these. "Any one who hopes to deduce from the chemical and physical properties of the fertilised egg the necessity that an animal, tormented by hunger and love must, after a certain time, arise therefrom, has a pathetic resemblance to the miserable manufacturers of homunculi." Life is one of the underivable and inexplicable fundamental functions of universal being. From all eternity life has only been produced from life.

As Preyer accepts the Kant-Laplace theory of the origin of our earth from the sun, he reaches ideas which have points of contact with the "cosmo-organic" ideas of Fechner. Life was present even when the earth was a fiery fluid sphere, and was possibly more general and more abundant then than it is now. And life as we know it may only be a smaller and isolated expression of that more general life.(80)

Among the younger generation of specialists, those most often quoted as opponents of the mechanical theory are probably Bunge, Rindfleisch, Kerner von Marilaun, Neumeister and Wolff. A special group among them, not very easy to cla.s.sify, may be called the Tectonists. a.s.sociated with them is Reinke's "Theory of Dominants." Driesch started from their ranks, and is a most interesting example of consistent development from a recognition of the impossibilities of the mechanistic position to an individually thought-out vitalistic theory. Hertwig, too, takes a very definite position of his own in regard to these matters. Perhaps the most original contribution in the whole field is Albrecht's "Theory of Different Modes of Regarding Things." We may close the list with the name of K. C.

Schneider, who has carried these modern ideas on into metaphysical speculation. Several others might be mentioned along with and connecting these representative names.(81)

The Position Of Bunge and Other Physiologists.

For a long time one of the most prominent figures in the controversy was Prof. G. Bunge, of Basle, who was one of the first modern physiologists to champion vitalism, and who has tried to show by a.n.a.logies and ill.u.s.trations what is necessarily implied in vital activity.(82) The mechanical reduction of vital phenomena to physico-chemical forces, he says, is impossible, and becomes more and more so as our knowledge deepens. He brings forward a series of convincing examples of the way in which apparent mechanical explanations have broken down. The absorption of the chyle through the walls of the intestine seemed to be a mechanically intelligible process of osmosis and diffusion. But in reality it proves to be rather a process of selection on the part of the epithelial cells of the intestine, a.n.a.logous to the selection and rejection exercised elsewhere by unicellular organisms. In the same way the epithelial cells of the mammary glands "select" the suitable substances from the blood. It is impossible to explain in a mechanical way the power which directs the innumerable different chemical and physical processes within the organism, whether they be the bewilderingly purposeful reactions in the individual life of the cell, which seem to point to psychic processes within the plasm, or the riddles of development and of inheritance in particular; for how can a spermatozoon, so small that 500 millions can lie on a cubic line, be the bearer of all the peculiarities of the father to the son?

In Lecture III. Bunge defines his att.i.tude towards the law of the conservation of energy. In so doing he unconsciously follows the lines laid down by Descartes. All processes of movement and all functions exhibited by the living substance are the results of the acc.u.mulated potential energies, and the sums of work done and energy utilised remain the same. But the liberation and the direction of these energies is a factor by itself, which neither increases nor diminishes the sum of energies. "_Occasiones_" and "_causae_" are brought into the field once more. The energies effect the phenomena, but they require "_occasiones_"

to liberate them-thus a stone may fall to the ground by virtue of the potential energies stored in it at the time of its suspension, but it cannot fall until the thread by which it hangs has been cut. The function of the "_occasio_" itself is something quite outside of and without relation to the effect caused; it is a matter of indifference whether the thread be cut gently through with a razor or shot in two with a cannon ball.

Ka.s.sowitz(83) is an instructive example of how much the force of criticism has been recognised even by those occupying a convinced mechanical point of view. He subjects all the different theories which attempt to explain the chief vital phenomena in mechanical terms to a long and exhaustive examination. The theories of the organism as a thermodynamic engine, osmotic theories, theories of ferments, interpretations in terms of electro-dynamics and molecular-physics-are all examined (chap. iv.); and the failure of all these hypotheses, notwithstanding the enormous amount of ingenuity expended in their construction, is summed up in an emphatic "_Ignoramus_." "The failure is a striking one," and it is frankly admitted that, in strong contrast to the earlier mood of confident hope, there now prevails a mood of resignation in regard to the mechanical-experimental investigation of the living organism, and that even specialists of the first rank are finding that they have to reckon again seriously with vital force. This breakdown and these admissions do not exactly tend to prejudice us in favour of the author's own attempt to substantiate new mechanical theories.

In the comprehensive text-book of physiological chemistry by R.

Neumeister, the mechanical standpoint seemed to be adhered to as the ideal. But the same writer forsakes it entirely, and disputes it energetically in his most recent work, "Betrachtungen uber das Wesen der Lebenserscheinungen"(84) ("Considerations as to the Nature of Vital Phenomena"). He pa.s.ses over all the larger problems, such as those of development, inheritance, regeneration, and confines himself in the main to the physiological functions of protoplasm, especially to those of the absorption of food and metabolism. And he shows, by means of ill.u.s.trations, in part Bunge's, in part his own, and in close sympathy with Wundt's views, that even these vital phenomena cannot possibly be explained in terms of chemical affinity, physical osmosis, and the like.

In processes of selection (such as, for instance, the excretion of urea and the retention of sugar in the blood), the "aim is obvious, but the causes cannot be recognised." Psychical processes play a certain part in the functions of protoplasm in the form of qualitative and quant.i.tative sensitiveness. All the mechanical processes in living organisms are initiated and directed by psychical processes. Physical, chemical and mechanical laws are perfectly valid, but they are not absolutely dominant.

Living matter is to be defined as "a unique chemical system, the molecules of which, by their peculiar reciprocal action, give rise to psychical and material processes in such a way that the processes of the one kind are always causally conditioned and started by those of the other kind." The psychical phenomena he regards as transcendental, supernatural, "mystical," yet unquestionably also subject to a strict causal nexus, although the causality must remain for ever concealed. Starting from this basis, he a.n.a.lyses and rejects the explanations which have been offered in terms of the a.n.a.logy of ferments, enzymes, or catalytic processes. In particular, he disputes Ostwald's "Energismus" and Verworn's Biogen hypothesis.(85)

Among the vitalists of to-day, one of the most frequently cited, perhaps, except Driesch the most frequently cited, is G. Wolff, a _Privatdozent_, formerly at Wurzburg, now at Basle. He has only published short lectures and essays, and these deal not so much with the mechanical theory as with Darwinism.(86) But in these writings his main argument is that of his concluding chapter: the spontaneous adaptiveness of the organism, which nullifies all contingent theories to explain the purposiveness in ontogeny and phylogeny. And in his lecture, "Mechanismus und Vitalismus,"(87) in which he directs his attention especially to criticising Butschli's defence of mechanism, the only problem to which prominence is given is the one with which we are here concerned. In spite of their brevity, these writings have given rise to much controversy, because what is peculiar to the two standpoints is described with precision, and the problem is clearly defined. His criticism had its starting-point in, and received a special impulse from an empirical proof, due to a very happy experiment of his own, of the marvellous regenerative capacity, and the inherent purposive activity of the living organism. He succeeded in proving that if the lens of the eye of the newt be excised, it may be regrown. The importance of this fact is greatly increased if we trace out in detail the various impossible rival mechanical interpretations which have grown up around this interesting case. As Driesch says, "It is not a restoration starting from the wound, it is a subst.i.tution starting from a different place."

The Views of Botanists Ill.u.s.trated.

It might have been expected that in the domain of plant-biology, if anywhere, the mechanistic standpoint would have been the prevailing one.

For it is almost a matter of course to regard plants as devoid of sensation or "psychical" life, and as mechanical systems, chemical laboratories, and reflex mechanisms, and this way of regarding them has been made easy by the very marked uniformity and lack of spontaneity in their vital processes as compared with those of animals. But it is not the case that mechanical theories have here prevailed. The opposition to them is just as great here as elsewhere, and from the days of Wigand onwards it has been almost continuously sustained.(88) Very characteristic is Pfeffer's "Pflanzen-Physiologie" (1897), which is written professedly from the mechanist point of view. "Vitalism," according to this authority, is to be rejected, but instead of "vital force" he offers us "given properties," and the alleged machine-like collocations of the most minute elements. In regard, for instance, to the riddle of development and morphogenesis, we must simply accept it as a "given property," that the acorn grows in an oak and nothing else. The chemical explanation of the vital functions of protoplasm is also to be rejected; as a shattered watch is no longer a watch though it remains chemically the same, so it is with protoplasm. The available chemical knowledge of the substances of which protoplasm is made up is insufficient to render the vital processes intelligible. Here, as everywhere else, we have to reckon with ultimate "properties (ent.i.ties), which we neither can, nor desire to a.n.a.lyse further." "The human mind is no more capable of forming a conception of the ultimate cause of things than of eternity." If all the views here indicated were followed out to their logical conclusions, they would hinder rather than further the process of reduction to terms of physico-chemical sequences.

Kerner von Marilaun in his "Pflanzenleben" deliberately takes up a thorough-going vitalist position, and on this point as well as on many others he opposed the current theory of the school (Darwinism). It is true, he admits, that many of the phenomena in plants can be explained in purely mechanical terms, but they are only those which may occur also in non-living structures. The specific expressions of life cannot be explained in this way. He shows this more fully in regard to the most fundamental of all the vital processes in the plant-body-the breaking up of carbonic acid gas by the chlorophyll to obtain the carbon which is the fundamental element in all living organisms. We know the requisite conditions: the supply of raw material, and the sunlight from which the energy is derived. But how the chlorophyll makes use of these to effect the breaking up, and how it starts the subsequent syntheses of the carbon into the most complex organic compounds remains a mystery. And so on upwards through all the strictly vital phenomena.

Wiesner's(89) view of things is essentially similar. He gives a very impressive picture of the mystery of the chemistry of the plant, showing how small is the number of food-stuffs and raw materials in comparison to the thousands of highly complex chemical substances which the plant produces, and how much work there is involved in de-oxydising the food and in forming syntheses. He, too, refuses, as usual, to postulate "vital force." Yet to speak of "the fundamental peculiarities of the living matter inherent in the organism" and to admit that plants are "irritable,"

"heliotropic," "geotropic," &c., amounts to much the same thing as postulating vital force; that is to say, to a mere naming of the specific problem of life without explaining it. The author himself admits this when he says in another place: "If I compare organisms with inorganic systems, I find that the progress of our knowledge is continually enlarging the gulf which separates the one from the other!"

These anti-mechanical tendencies show themselves most emphatically in the work of Fr. Ludwig.(90) In his concluding chapter, after a discussion of the theories of Darwin, Nageli, and Weismann, he postulates, for variation, heredity, and species-formation in particular, "forces other than physico-chemical," "let us call them frankly psychical."

It is instructive to see how these "vitalistic" views crop up even in studies of detail and of the microscopically small, as for instance in E.

Crato's "Beitrage zur Anatomie und Physiologie des Elementar-organismus."

How the living organism contains within itself what is in its turn living, down into ever smaller detail, (amboid movements of certain plastines, physodes,) how incomparable the living organism is with a "machine," to which its libellers are so fond of likening it, how it builds itself up, steers, and stokes itself, how it produces with "playful ease" the most marvellous and graceful forms, makes combinations and breaks them up, how a.n.a.logous its whole activity is to "being able" and "willing," all this is clearly brought out.(91)

A very fresh and lucid presentation of the whole case is given by Borodin, Professor of Botany in St. Petersburg, in his essay, "Protoplasm and Vital Force."(92) He sharply castigates the one-sidedness and impetuosity of the mechanical theory, as in Haeckel's discovery of Bathybius and of non-nucleated bacteria. The latter are problematical, and the former has been proved an illusion. To penetrate farther into the processes of life is simply to become aware of an ever-deepening series of riddles. There is no such thing as "protoplasm," or "living proteid," or indeed any unified, simple "living matter" whatever. Artificial "oil-emulsion amoebae"(93) bear the same relation to living ones that Vaucanson's mechanical duck bears to a real one; that is, none at all. Our "protoplasm" is as mystical as the old "vital force," and both are only camping-grounds for our ignorance.

Neither the mechanical nor the atomic theory were the results of exact investigations; they were borrowed from philosophy. We do indeed investigate the typically vital process of irritability by physical methods. But the response made by the organism to physical coercion may be called a mockery of physics. The mechanists help themselves out with crude a.n.a.logies from the mechanical, conceal the problem with the name "irritability," and thus get rid of the greatest marvels. If vital force itself were to call out from its cells, "Here I am," they would probably see in it only a remarkable case of "irritability." Mechanism is no more positive knowledge than vitalism is; it is only the dogmatic faith of the majority of present-day naturalists.

Constructive Criticism.

Those whose protests we have hitherto been considering have not added to their criticism of the mechanical theory any positive contribution of their own, or at least they give nothing more than very slight hints pointing towards a psychical theory. But there are others who have sought to overcome the mechanical theory by gaining a deeper grasp of the nature of "force" in general. Their attempts have been of various kinds, but usually tend in one direction, which can perhaps be most precisely and briefly indicated through Lloyd Morgan's views, as summed up, for instance, in his essay on "Vitalism."(94) In the beginning of biological text-books, we usually find (he says) a chapter on the nature of "force,"

but it is "like grace before meat"-without influence on quality or digestion. Yet this problem must be cleared up before we can arrive at any understanding of the whole subject. In all attempts at "reducing to simpler terms," it must be borne in mind that "force" reveals its nature in ever higher stages, of which every one is new. Even cohesion cannot be reduced to terms of gravitation, nor the chemical affinities and molecular forces to something more primitive. They are already something "outside the recognised order of nature." In a still higher form force is expressed in the processes of crystallisation. At the formation of the first crystal there came into action a directing force of the same kind as the will of the sculptor at the making of the Venus of Melos. This new element, which intervenes every time, Lloyd Morgan regards, with Herbert Spencer ("Principles of Biology"), as "due to that ultimate reality which underlies this manifestation, as it underlies all other manifestations."

There can be no "understanding" in the sense of "getting behind things": even the actions of "brute matter" cannot be "understood." The play of chance not only does not explain the living; it does not even explain the not-living. But life in particular can neither be brought into the cell from without, nor be explained as simply "emerging from the co-operation of the components of the protoplasm," and it is "in its essence not to be conceived in physico-chemical terms," but represents "new modes of activity in the noumenal cause," which, just because it is noumenal, is beyond our grasp. For only phenomena are "accessible to thought."

Among the biologists who concern themselves with deeper considerations, Oscar Hertwig,(95) the Director of the Anatomical Inst.i.tute at Berlin, has expressed ideas similar to those we have been discussing, little as this may seem to be the case at first sight. He desires to oust the ordinary mechanism, so to speak, by replacing it by a mechanism of a higher order, and in making the attempt he examines and deepens the traditional ideas of causality and "force," and defines the right and wrong of the quant.i.tative-mathematical interpretation of nature in general, and of mechanics in particular. He follows confessedly in Lotze's path, not so much in regard to that thinker's insistence upon the a.s.sociation of the causal and the teleological modes of interpretation, as in modifying the idea of causality. O. Hertwig puts forward his own theories with special reference to those of W. Roux, the founder of the new "Science of the Future"-the mechanical, and therefore only scientific theory of development, which no longer only describes, but understands and causally explains phenomena ("Archiv fur Entwicklungsmechanik"). There are two kinds of mechanism (Hertwig says): that in the higher philosophical sense, and that in the purely physical sense. The former declares that all phenomena are connected by a guiding thread of causal connection and can be causally explained. As such, its application to the domain of vital phenomena is justifiable and self-evident. But it is not justifiable if cause be simply made identical with and limited to "force," if the causal connection be only admitted in the technical sense of the transference and transformation of energy, and if, over and above, it is supposed to give an "explanation," in the sense of an insight into things themselves. Even mechanics is (as Kirchoff maintained) a "descriptive" science. Hertwig agrees with Schopenhauer and Lotze in regarding every primitive natural "force" as unique, not reducible to simpler terms, but qualitatively distinct,-a "qualitas occulta," capable not of physical but only of metaphysical explanation. And thus his conclusions imply rejection of mechanism in the cruder sense. As such, it has only a very limited sphere of action in the realm of the living. The history of mechanical interpretations is a history of their collapse. The attempt to derive the organic from the inorganic has often been made. But no such attempts have held the field for long. We can now say with some reason that "the gulf between the two kingdoms of nature has become deeper just in proportion as our physical and chemical, our morphological and physiological knowledge of the organism has deepened." Mach's expression "mechanical mythology,"

is quoted, and then a fine pa.s.sage on the insufficiency of the mathematical view of things in general concludes thus: "Mathematics is only a method of thought, an excellent tool of the human mind, but it is very far from being the case that all thought and knowledge moves in this one direction, and that the content of our minds can ever find exhaustive expression through it alone."

In his "Theory of Dominants,"(96) Reinke, the botanist of Kiel, has attempted to formulate his opposition to the physico-chemical conception of life into a vitalistic theory of his own. Among biologists who confess themselves supporters of the mechanical theory, there are some who expressly reject explanations in terms of chemical and physical principles, and emphasise, more energetically than others, that these can only give rise to vital phenomena and complex processes of movement, on the basis of a most delicately differentiated structure and architecture of the living substance in its minute details, and from the egg onwards.

They have created the strict "machine theory," and they may be grouped together as the "tectonists." "A watch that has been stamped to pieces is no longer a watch." Thus the merely material and chemical is not the essential part of the living; it is the tectonic, the machinery of structure that is essential. The fundamental idea in this position is precisely that of Lotze. It is not a "mystical," vital principle, that sets up, controls, and regulates the physical and chemical processes within the developed or developing organism. They receive their direction and impulse through the fact that they are a.s.sociated with a given peculiar mechanical structure. This theory certainly contains all the monstrosities of preformation in the germ, the mythologies of the infinitely small, and it suffers shipwreck in ways as diverse as the number of its sides and parts. But it has the merit of clearly disclosing the impossibilities of purely chemical explanations. Reinke's "Theory of Dominants" started from such tectonic conceptions, and so originally did Driesch's Neovitalism, of which we shall presently have to speak.

Reinke's theory has gone through several stages of development. At first its general tenor was as follows: Every living thing is typically different from everything that is not living. What explains this difference? Certainly not the hypothesis of vital force, which is far from being clear. The idea that forces of a psychic nature are inherent in the organism is also rejected. The ill.u.s.tration of a watch helps us to understand. The impelling force in it is certainly not merely the ordinary force of gravity or the general elasticity of steel. The efficacy of simple forces such as these can be increased in infinite diversity by the "construction of the apparatus" in which they operate. Life is the function of a quite unique, marvellously complex, inimitable combination of machines. If these be given, the most complex processes fulfil themselves of necessity and without the intervention of special vital forces. But how can they be "given"? The sole a.n.a.logy to be found is the making of real machines, artificial products as distinguished from fortuitous products. They cannot be made without the influence and activity of intelligence. To explain the incomparably more ingenious and complex vital machine as due to a fortuitous origin and collocation of its individual parts would be more absurd than it would be to think of a watch being made in this way. The dominance of a creative idea cannot but be recognised. An intelligent natural force which is conscious of its aims and calculates its means must be presupposed, if we are really to satisfy our sense of causality. It is a matter of personal conviction whether we find this force in "G.o.d" or in the "Absolute."

These views are more fully developed in the theory of dominants expounded in Reinke's later work, "Die Welt as Tat" (after what has been said the meaning of the t.i.tle will be self-evident), and in his "Theoretische Biologie."(97) Very vigorous and convincing are the author's objections to the naturalistic theories of organic life, especially to the "self-origin"

of the living, or spontaneous generation. In all vital processes we must reckon with a "physiological _x_," which cannot be eliminated, which gives to life its unique and underivable character. There are "secondary forces," "superforces," "dominants," which bring about what is peculiar in vital functions and direct their processes. "Vitalism" in the strict sense is thus here also rejected. The machine-theory is held valid. There are "dominants" even in our tools and utensils, in our hammer and spoon, and the "operation" of these cannot be explained merely physico-chemically, but through the dominants of the form, structure and composition, with which they have been invested by intelligence. The a.s.sociation with the views of the tectonists is so far quite apparent. But the idea of "dominants" soon broadens out. We find dominants of form-development, of evolution, and so on. What were at first only peculiarities of structure and architecture have grown almost unawares into dynamic principles of form which have nothing more to do with the mechanical theory, and which, because of their dualistic nature, result in conclusions and modes of explanation which can hardly be called very useful. The lines along which the idea has developed are intelligible enough. It started originally from that of the organism as a finished product, functioning actively, especially in its metabolism. Here the comparison with a steam engine with self-regulators and automatic whistles is admissible, and one may speak of dominants in the sense of mechanical dominants. But the idea thus started was pressed into general service. And thus arose dominants of development, of morphogenesis, even of phylogenetic evolution ("phylogenetic evolution-potential"). New dominants are added, and the theory advances farther and farther from the "machine theory," becomes ever more enigmatical, and more vitalistic.