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The very justifiable surprise which Virchow’s Munich address has excited in many circles is due only in part to his opposition to the theory of descent; for the rest, and in much greater part, it is due to the astounding arguments which he has connected with it, particularly as to freedom for instruction. These arguments so closely resemble those of the Jesuits that they might have been inspired direct from the Vatican, or, which is the same thing, the notorious “court-chaplain party” in Berlin. No wonder, then, that these propositions, which would undermine the whole liberty of science, have met with the loudest approbation from the “Germania,” the “New Evangelical Church Times” ("Neue Evangelischen Kirchenzeitung"), and other leading, equivocating organs of the Church militant. On the other hand, these odious principles are already so extensively discussed, and have been so clearly laid down in all their indefensibility, that I may here deal with them briefly.

Virchow’s politics as a pedagogue reach their highest pitch in this demand: “that in all schools, from the poor schools to the universities, nothing shall be taught that is not absolutely certain. None but objective and absolutely ascertained knowledge is to be imparted by the teacher to the learner; nothing subjective, no knowledge that is open to correction, only facts, no hypotheses.” The investigation of such problems as the whole nation may be interested in must not be restricted; that is liberty of inquiry; but the problem ought not, without anything farther, to be the subject of teaching. “When we teach we must restrict ourselves to the smaller, and yet how great, departments which we are actually masters of.”

Rarely indeed has such a treasonable attempt on liberty of doctrine been made by a prominent representative of science, and a leader of the intellectual movement too, as this by Virchow. Only inquiry is to be free and not teaching! And where in the whole history of science is there one single scientific inquirer to be found who would not have felt himself quite justified in teaching his own subjective convictions with as much right as he had to construct them from inquiry into objective facts. And where, generally speaking, is the limit to be found between objective and subjective knowledge? Is there, in fact, any objective science?

This question Virchow answers in the affirmative, for he goes on to say: “We must not forget that there is a boundary line between the speculative departments of natural science and those that are actually conquered and firmly established” . In my opinion, there is no such boundary line; on the contrary, all human knowledge as such is subjective. An objective science which consists merely of facts without any subjective theories is inconceivable. For evidence in favour of this view we must take a rapid survey of the whole domain of human science, and test the chief departments of it to see how far they contain, on the one hand, objective knowledge and facts, and on the other, subjective knowledge and hypotheses. We may begin directly with Kant’s assertion that in every science only so much true that is objective knowledge is to be found as it contains of mathematics. Unquestionably mathematics stand at the head of all the sciences as regards the certainty of its teaching. But how as to those deepest and simplest fundamental axioms which constitute the firm basis on which the proud edifice of mathematical teaching rests? Are these certain and proved? Certainly not. The bases of its teaching are simply “axioms” which are incapable of proof. To give only one example of how the very first principles of mathematics might be attacked by scepticism and shaken by philosophical speculation, we may remember the recent discussions as to the three dimensions of space and the possibility of a fourth dimension; disputes which are carried on even at the present day by the most eminent mathematicians, physicists, and philosophers. So much as this is certain, that mathematics as little constitute an absolutely objective science as any other, but by the very nature of man are subjectively conditioned. A man’s subjective power of knowing can only discern the objective facts of the outer world in general so far as his organs of sense and his brain admit in his own individual degree of cultivation.

However, granting that mathematics practically constitute an absolutely certain and objective science, how is it with the rest of the sciences? Undoubtedly the most certain among them are those “exact sciences” whose principles are to be directly proved by mathematics; thus, in the first place, a great part of physics. We say, “a great part,” for another large part to speak accurately, by far the greatest is incapable of any exact mathematical proof. For what do we know for certain of the essential nature of matter, or the essential nature of force? What do we know for certain of gravitation, of the attraction of mass, of its effects at great distances, and so on? Newton’s theory of gravitation is regarded as the most important and certain theory of physics, and yet gravitation itself is a hypothesis. Then, as to the other branches of physics electricity and magnetism. The whole scheme of these important sciences rests on the hypothesis of “electric fluidity,” or of imponderable matter of which the existence is nothing less than proved. Or optics? Optics certainly appertain to the most important and completest branch of physics, and yet the undulatory theory of light, which we accept now as the indispensable basis of optics, rests on an unproved hypothesis, on the subjective assumption of an ethereal medium, whose existence no one is in a position to prove objectively in any way. Nay, further, before Young set up the undulatory theory of light, for a hundred years the emanation theory as taught by Newton obtained exclusively in physics; a theory which at the present day is universally regarded as untenable. In our opinion the mighty Newton won the greatest honours in the development of the science of optics, inasmuch as he was the first to connect and explain the vast mass of objective optical facts by a subjective and pregnant hypothesis. But, according to Virchow’s view, Newton on the contrary transgressed greatly by teaching this erroneous hypothesis; for even in “exact” physics none but “independent and certain facts” are to be taught and established by “experiment as the highest means of proof.” Physics as a whole, as resting on mere unproved hypotheses, may be indeed an object of inquiry but not of teaching.

Of course the same is true of chemistry; nay, this stands on much weaker feet, and is even less proved than physics. The whole theoretical side of chemistry is an airy structure of hypotheses such as does not exist in any other science. In the last three decades we have seen a whole series of the most different theories rapidly succeed each other, none of which can be positively proved, though at least one of them is taught by every professor of chemistry. But what is worst of all, the common basis of all the most dissimilar chemical theories, viz., the atomic theory, is as unproved and unprovable as any hypothesis can be. No chemist has ever seen an atom, but he nevertheless considers the mechanism of atoms as the highest term of his science, he nevertheless describes and constructs the connection of atoms in their various combinations as though he had them before him on the dissecting-table! All the conceptions which we possess as to chemical structure and the affinities of matter, are subjective hypotheses, mere conceptions as to the position and changes of position of the various atoms, whose very existence is incapable of proof. Away, then, with chemistry from our schools! The chemist must only describe the properties of the different elements and those combinations which can be put before the pupil as ascertained facts founded in experiment, “the highest means of proof.” Everything that goes beyond this is mischievous, particularly every suggestion as to the essence and chemical constituents of bodies; matters as to which, in the nature of things, we can only form uncertain hypotheses. For as all chemistry, viewed as a system of doctrine, rests solely on such hypotheses, it may be indeed a subject of investigation but not of teaching.

Having thus convinced ourselves that chemistry as well as physics, those “exact sciences,” those “mechanical” bases of all other sciences, rest on mere unproved hypotheses, and so must not be taught, we may make short work of the other faculties. For they collectively are more or less historical sciences and dispense wholly or in part with even those half-exact, fundamental principles on which physics and chemistry are based. In the first place, there is that grand, historical, natural science, geology; the great doctrine of the structure and composition, the origin and development of our globe. According to Virchow this too must be limited to the description of ascertained facts, such as the structure of mountain masses, the character of the fossils they contain, the formation of crystals, and so forth. But not for the world must anything be taught as to the evolution of this globe; for this rests from beginning to end on unproved hypotheses. For even to the present day the Plutonic and Neptunic theories are disputing the field, and to this day we know not as to many of the most important rocks, whether they originated by the agency of fire or of water. The new and remarkable discoveries of the great Challenger-expedition threaten to subvert a great many geological notions which had long been regarded as certain. Then again, as to fossils. Who can prove with any certainty that these petrifactions are in truth the fossilised remains of extinct organisms? They may be as many distinguished naturalists of even the last century maintained marvellous sports of nature, mysterious “Lusus naturae,” or mere rough, inorganic models of the labouring Creator into which He subsequently “breathed the breath of life;” or perhaps “stone-flesh” (caro fossilis) brought into existence, on the dead rocks by the “fertilising air” (aura seminalis), and so forth.

But I am wrong! for with regard to petrifactions, Virchow is in the highest degree speculative, and accepts without any hesitation the rash hypothesis that fossils are actually the remains of extinct organisms, although no “certain proof” whatever can be offered in its favour, and although experiment, the “highest means of proof,” has never yet produced a single fossil. According to him these are actual “objective, material evidences,” only here we must go no further than certain experience teaches us, and base no subjective conclusions on these objective facts. Thus, for instance, in the long series of the mesozoic formations, in the different strata of the Trias, Jurassic, and Chalk formations, for the deposition of which a lapse of many millions of years has been required, we find absolutely no remains of fossil mammalia beyond lower jaws; seek where we will, nothing is anywhere to be found but lower jaws, and no other bones whatever. The simple reasons of this striking imperfection of the palaeontological record have been clearly expounded by Lyell, Huxley, and others. (Comp. my “History of Creation,” vol. ii. .) These great investigators, in accordance with all other palaeontologists, have demonstrated that these jaw-bones of the mesozoic period are the remains of mammalia, accurately speaking of marsupials, on the simple ground that the nether jaws of the extant recent marsupials show a similar characteristic form with the fossil ones. They therefore unhesitatingly assume that the rest of the bones in the bodies of these extinct animals corresponded to those of living mammals. But this is a quite inadmissible hypothesis devoid of any “certain proof!” Where, then, are the other bones? Let us see them! till then we decline to believe in them. According to Virchow, we ought rather to assume that the lower jaw was the only bone in the body of these extraordinary beasts. Are there not, in fact, snails, in which an upper jaw is the only representation of a skeleton.

We cannot omit taking this opportunity of casting a side glance at the very hazardous position which Virchow, in total opposition to his boasted cool scepticism, has taken up in anthropology as it is called, now his favourite branch of science. In his Munich address he tells us that he is pursuing the study of anthropology with delight, and then asserts that “the quarternary man” is an universally-accepted fact. Quite apart from this statement, we have seen that Virchow can never attain to a profound and really scientific study of anthropology simply for this reason, that he is lacking in that comprehensive knowledge of comparative morphology which is indispensable to it; nay, comparative anatomy and ontogenesis must be, according to him, unpermitted speculations and the phylogenesis of man, the key to all the most important questions of anthropology, being based upon these, is devoid of all certain proof. All the more must we wonder at the speculative levity with which even the sceptic Virchow in the “Primeval History of Man” and “Fossil Anthropology,” embarks in the most hazardous conjectures, and gives out uncertain, subjective hypotheses as certain, objective facts.

There is, in fact, at the present day no department of science in which the wildest and most untenable hypotheses have blossomed out so freely as in anthropology and ethnology, so-called. All the phylogenetic hypotheses which I myself have put forward in my “Evolution of Man” as to the animal ancestry of man, or in my “Natural History of Creation” as to the affinities of animal races all the other genealogical hypotheses which are now advanced by numerous zoologists and botanists as to the phylogenetic evolution of the animal and plant worlds all these hypotheses together, which Virchow rejects in a lump, are, critically considered as hypotheses, far better grounded in facts, far better supported by facts, than the majority of those innumerable airy and fanciful hypotheses with which, for the last twelve years, the “Archiv fuer Anthropologie” and “Zeitschrift fuer Ethnologie,” edited by Virchow and Bastian, have filled their columns. This last periodical has at least the merit of being a tolerably consistent opponent of the doctrine of evolution, while in the former, during twelve years, essays on both sides have been mixed up in cheerful confusion. And how fanciful are the short-sighted hypotheses which there blossom forth from the mixed mass of facts, chaotically flung together. Only think of the disputes over the stone age, bronze age, and iron age; think of the motley discussions as to the varieties of skull-conformation and their significance; on the races of man, the migrations of peoples and the like. Most of these very intricate historical problems are far more buried in obscurity, and the hypotheses to explain them dispense far more largely with any basis of facts, than is the case with our phylogenetic hypotheses; for these are more or less “objectively” based on the facts of comparative anatomy and ontogenesis.

But no one of these historical hypotheses is so daring, so little “certainly proved,” as the group of very various and contradictory hypotheses which have been put forward as to the antiquity and first appearance of the human species; and Virchow asserts positively “The pléistocène man is an universally accepted fact. The tertiary man is, on the other hand, a problem, though indeed a problem which is already under substantial discussion!” As if the distinction between the tertiary and quarternary periods were not itself a geological hypothesis, and as if the significance of the fossil animal-remains, which play the largest part in it, did not also rest on mere hypotheses which escape all certain proof! Where, then, is the actual experiment “as the highest means of proof,” which gives evidence for these “certain facts”? The whole discussion in general about prehistoric man, which Virchow has mixed up with his Munich address (pp. 30, 31), is the clearest evidence of the uncritical spirit in which he deals with these historical problems as “exact natural sciences.” He assures us that “not one single ape’s skull, nor skull of an anthropoid ape, has ever been found which could actually have belonged to a human owner!” and he adds this sentence, in italics, “We cannot teach, for we cannot regard it as a real acquisition of science, that man is descended from the ape or from any other animal!” Then evidently no alternative remains but that he is descended from a god, or from a clod!

But let us go over the rest of the sciences to see what, according to Virchow, may be taught in each without endangering the safety of science. In the whole department of biology, as well as in zoology including anthropology and in botany, instruction must be limited to imparting those trifling fragments of knowledge which either consist of mere descriptions of dry facts, or which supply an explanation of them by mathematical formulas. Morphology must be taught as mere descriptive anatomy and systematising, the history of development as mere descriptive ontogenesis. Comparative anatomy and phylogenesis, which by their explanatory hypotheses raise those dead masses of facts to the place of true and living sciences these must not be taught at all. And how then do matters stand with regard to the cell-theory, that fundamental theory on which every element of our morphology and physiology depends, and by applying which Virchow himself reached his grandest results?

Since Schleiden in Jena, forty years ago, first put forward the cell-theory, and Schwann immediately after applied it to the animal kingdom and so to the whole organic world, this fundamental doctrine has undergone very important modifications, for it is indeed a biological theory, but not a fact. We may recollect under what different aspects its main principles have appeared in the course of these four decades: what changes have taken place in the conception of the cell itself. After the organic cell had originally been conceived of as a vesicle, consisting of a firm capsule and a fluid content, we subsequently discerned it to be composed of a glutinous semi-fluid cell-substance, the protoplasm, and convinced ourselves that this protoplasm and the cell-core or nucleus enclosed in it are the most important and indispensable constituent parts of the cell, while the external firm capsule, the cell-membrane, is not essential and very frequently wanting. But even now opinions widely differ as to how the conception of a cell should be precisely defined, and what consequences must be inferred from the cell-theory, and attempts have not been wanting to upset it altogether and to treat it as worthless. The anatomist Henle, of Goettingen, in particular, has repeatedly made such an attempt, that “gifted” anatomist who, in the preface to his bulky text-book of human anatomy, declared that scientific ideas are mere worthless paper money, and that the noble metal of facts, on the contrary, is the only genuine article. Not long since a bulky volume in quarto appeared, by one Herr Nathusius-Koenigsborn, in which the cell is explained to be a subordinate plastic element, and the cell-theory is eliminated as superfluous; and this monstrous volume, full of the most amusing nonsense, is dedicated to Herr Henle. Virchow formerly was one of the victorious opponents of the Goettingen physician, and wrote brilliant articles against the “rational pathology” of “irrational Herr Henle;” now apparently he agrees with him that the paper money of ideas is worthless as compared with the noble metal of facts. Of course the cell-theory then loses all its value, and cannot be a subject of instruction; for the cell itself is not a certain and undoubted fact, but only an abstraction, a philosophical idea.

Nothing more clearly shows what a complete change Virchow has undergone in his most important principles, and what an utter metapsychosis in this special province, than his famous axiom, uttered in 1855 “Omnis cellula e cellula.” That is unquestionably the boldest generalisation to which the youthful, independent Virchow ever attained, and one on which he justly prided himself not a little. He himself repeatedly compared it with Harvey’s saying, which marked an epoch “Omne vivum ex ovo.” But neither of these axioms is universally correct. On the contrary, we now know that every cell does not necessarily originate from a cell, any more than that every organic individual originates from an ovum. In many cases true nucleated cells proceed from un-nucleated cytods, as in the Gregarinae, Myxomycetae and others. Nay more, the primordial organic cells could only have originated in the first instance from non-cellular plastides or monads by their homogeneous plasson resolving itself into an internal nucleus and an external protoplasm. Thus, as we subsequently learnt to know most of the exceptions to this generalisation of Virchow, it appeared all the bolder; the more so as we were at that time far from being able to refer all the different tissues of the higher animals with any certainty to cells, and as not a few experiments seemed to point to the hypothesis of free cell-formation. That guiding axiom, which so powerfully furthered the cell-theory, Virchow, from his present standpoint, must wholly condemn as a crime against exact science, and he surely can never forgive himself for having propounded this hypothesis which was afterwards found to be not universally true as an important doctrinal axiom.

We shall indeed find much worse sins against his own principles of to-day if we turn to Virchow’s own special department of science, namely, pathological anatomy and physiology, the most important division of theoretic medicine. The great and incomparable services which Virchow here effected do not depend on the numerous independent new facts which he discovered, but on the theories and hypotheses by which, like an inspired pioneer, he sought to open a way through the dead waste of pathological knowledge and to form it into a living science. These new theories and the hypotheses on which they were founded, Virchow then propounded to us, his disciples, with such incisive assurance that every one of us was convinced of their truth; and yet later experience has shown that they were in part insufficiently proved and in part wholly false. For example, I will only here recall his famous theory of the connective-tissue, for which I myself in several of my early works (1856 to 1858) broke a lance. His theory seemed to explain a host of the most important physiological and pathological phenomena in the simplest manner, and yet it was afterwards proved to be false. In spite of this, I declare to this day that it was of the greatest service for the development of our acquaintance with the formation of the connective-tissue; as a guiding hypothesis and as a provisional clue to our investigations. Virchow, on the contrary, if he impartially reflects on the part he took in the diffusion of this misleading doctrine, must reproach himself severely for it. For “we must draw a hard and fast line between what we are to teach and what we are to investigate. What we investigate are problems,” but “the problem ought not to be the subject of teaching.” That Virchow, in his course of instruction, every day belied this, his present view of teaching, that he every hour taught his disciples some unproved theory and problematical hypothesis, every one knows who, like myself, for years and with the deepest interest, enjoyed his distinguished instruction. Still the captivating charm of this instruction in spite of the defective method of unprepared lectures lay precisely in this, that Virchow as a teacher constantly let us, his pupils, enter into those problems with which he himself at the moment was occupied; that he propounded to us his personal hypothesis for the elucidation of the given facts. And what really gifted teacher who lives in his science would not do the same? Where is there, or where has there ever been, a great master who in his teaching has confined himself to only imparting certain and undoubtedly ascertained facts? Who has not, on the contrary, found that the charm and value of his instruction lay precisely in propounding the problems which link themselves with those facts, and in teaching the uncertain theories and fluctuating hypotheses which may serve to solve these problems? Or is there for the young and struggling mind anything better, or more conducive to culture, than to exercise the intelligence in problems of investigation?

How unpractical and how absurd is Virchow’s demand that only ascertained facts and no problematic theories shall be admitted in teaching will be still more strikingly shown by a glance over the remaining provinces of human knowledge. What, indeed, will be left of history, of philology, of political science, of jurisprudence, if we restrict the teaching of them to absolutely-ascertained and established facts. What of “science” will remain to them if the idea which endeavours to discern the causes of the facts is banished? if the problems, the theories, the hypotheses, which seek these causes may not be generally taught? And that philosophy the science of knowing by which all the common results of human knowledge are to be bound up into one grand and harmonious whole that philosophy, I say, must not be generally taught, is, according to Virchow, quite self-evident.

Finally, there remains nothing but theology. Theology alone is the one true science, and its dogmas alone may be taught as certain. Of course! for it proceeds directly from revelation, and only divine revelation can be “quite certain;” it alone can never err. Yes, incredible as it sounds, Virchow, the sceptical opponent of dogma, the leader of the fight for “liberty of science,” Virchow now finds the only sure basis for instruction in the dogmas of the Church. After all that has gone before, the following memorable sentence leaves no doubt on this score: “Every attempt to transform our problems into dogmas, to introduce our conjectures as a basis of instruction, particularly any attempt simply to dispossess the Church and to supplant her dogma by a creed of descent ay, gentlemen this attempt must fail, and in its ruin will entail the greatest peril on the position of science in general.”

The shouts of triumph of the whole clerical press over Virchow’s Munich address is thus rendered perfectly intelligible, for it is well known that “there is more joy in heaven over one sinner that repenteth than over ten just men.” When Rudolf Virchow, the “notorious materialist,” the “advanced radical,” the “great supporter of the atheism of science,” is so suddenly converted, when he proclaims loudly and publicly that the dogmas of the Church are the only sure basis of instruction, then the Church militant may well sing “Hosanna in the highest!” Only one thing is to be regretted, that Virchow has not more clearly defined which of the many different church-religions is the only true one, and which of the innumerable and contradictory dogmas are to form the sure basis of instruction. We all know that each Church regards itself as the only truly saving one, and her own dogma as the only true one. But as to whether it is to be Protestantism or Catholicism, the Reformed or the Lutheran confession, whether the Anglican or the Presbyterian dogma, whether the Roman or the Greek Church, the Mosaic or the Mohammedan dispensation, whether Buddhism or Brahmanism, whether, finally, it is to be one of the many fetish-religions of the Indians and Negroes that is to form the permanent and sure basis of instruction, let us hope that Virchow will at the next meeting of German naturalists and physicians divulge his opinion.

At any rate, the “instruction of the future, according to Virchow,” will be greatly simplified if he will do this. For the dogma of the Trinity in Unity as a basis of mathematics, the dogma of the resurrection of the body as a basis of medicine, the dogma of infallibility as a basis of psychology, the dogma of the immaculate conception as a basis of genetic science, the dogma of the staying of the sun as a basis of astronomy, the dogma of the creation of the earth, animals, and plants as a basis of geology and phylogenesis these or any other dogma, at pleasure, from any other church will make all other doctrine quite superfluous. Virchow, “that critical spirit,” knows as well as I, and as every other naturalist, that these dogmas are not true, and nevertheless, in his opinion, they are not to be supplanted as the “basis of instruction” by those theories and hypotheses of modern natural science of which Virchow himself says that they may be true, that in a great measure they probably are true, but are not yet “quite certainly proved.”

At pages 15, 24, 26, 28, and elsewhere in his Munich address, Virchow strongly insists that only that objective knowledge may be taught which we possess as absolutely certain fact! and then at page 29 he requires us to conclude that the basis of instruction shall continue to be the purely subjective dogmas of the Church; revelations and dogmas which not only are not proved by any facts whatever, but on the contrary, stand in the most trenchant contradiction to the most obvious facts of natural experience and fly in the face of all human reason. These contradictions, to be sure, are no greater than some others which stand out conspicuous and incomprehensible in Virchow’s discourse. Thus at the beginning of his address he glorifies Lorenz Oken and deeply laments “that he, that highly-valued and honoured master, that ornament of the high school of Munich, had been forced to die in exile! That cruel exile which oppressed Oken’s latter years, which left him to perish far from those cities to which he had sacrificed the best powers of his life, that exile will be remembered as the note of the time which we have passed through. And so long as there continue to be meetings of German naturalists, so long may we gratefully remember that this man to his death bore upon him all the signs of a martyr, so long shall we point to him as one of the witnesses who have fought for us and for the liberty of science.” Verily these words from Virchow’s lips sound like the bitterest irony; for was not Lorenz Oken one of the foremost and most zealous champions of that monistic doctrine of development against which Rudolf Virchow at this day is most violently striving? Did not Oken himself proceed farther in the construction of bold hypotheses and comprehensive theories than any supporter of the doctrine of evolution at the present time? Is not Oken justly considered as the one typical representative of that older period of natural philosophy who rose to much higher and bolder flights of fancy, and left the solid ground of facts much farther behind him than any tyro of the new philosophy? And this makes the irony seem all the greater with which Virchow at the beginning of his address glorifies Oken the free teacher, as a martyr to the freedom of science, and at the end of it insists that this freedom applies only to inquiry and not to teaching, and that the master must teach no problem, no theory, no hypothesis.

While this unheard-of demand sets Virchow’s views of teaching in the most extraordinary light, and while every unprejudiced and experienced teacher must most emphatically protest against this strait-waistcoat for instruction, he will feel no less bound to resist Virchow’s other strange demand, that every ascertained truth shall forthwith be taught in all schools, down to the elementary schools. I myself, in my Munich address, sought the instructional value of our monistic evolution theory above all in the genetic method, in the inquiry, that is to say, for the effective causes of the facts taught; and I added these words “How far the principles of the doctrine of universal evolution ought to be at once introduced into our schools, and in what succession its most important branches ought to be taught in the different classes cosmogony, geology, the phylogenesis of animals and plants, and anthropology this we must leave to practical teachers to settle. But we believe that an extensive reform of instruction in this direction is inevitable, and will be crowned by the fairest results.” I purposely avoided any closer discussion of this specialist question, as I felt not even approximately capable of solving it, and I believe, in fact, that none but skilled and experienced practical teachers can undertake the solution of it with any success.

For Virchow these specialist difficulties seem not to exist; he regards my reticence as a mere “postponement of the task,” and he answers in the following astonishing sentences: “If the theory of descent is as certain as Herr Haeckel assumes, then we must demand for it is a necessary consequence that it shall be taught in schools. How is it conceivable that a doctrine of such importance, which must effect such a total revolution in all our mental consciousness, which directly tends to create a new kind of religion, should not be included in the school scheme of instruction? How is it possible that such a revelation, shall I say should be in any measure suppressed, or that the promulgation of the greatest and most important advance which has been made in our views during the present century should be left to the discretion of schoolmasters? Ay, gentlemen, that would indeed be a renunciation of the hardest kind, and practically it could never be carried out! Every schoolmaster who assumes this doctrine for himself will involuntarily teach it, how can it be otherwise?”

I must here be permitted to take Virchow exactly at his word. I endorse almost all that he has said in these and the following sentences. The only difference in our views is this, that Virchow regards the theory of descent as an unproved and unproveable hypothesis; I, on the contrary, as a fully established and indispensable theory. How then will it be if the teachers of whom Virchow speaks agree with my views, if apart, of course, from all special theories of descent they, like me, consider the general theory of descent as the indispensable basis of all biological teaching? And that that is actually the case Virchow may easily convince himself if he looks over the recent literature of zoology and botany! Our whole morphological literature in particular is already so deeply and completely penetrated by the doctrine of descent, phylogenetic principles already prevail so universally as a certain and indispensable instrument of inquiry, that no man for the future would deprive himself of their help. As Oscar Schmidt justly observes “Perhaps ninety-nine per cent. of all living, or rather of all working zoologists, are convinced by inductive methods of the truth of the doctrine of descent.” And Virchow with his magisterial requirements will attain only the very reverse of what he aims at. How often has it not been said already that science must either have perfect freedom or else none at all? This is as true of teaching as it is of inquiry, for the two are intrinsically and inseparably connected. And so it is not in vain that it is written in section 152 of the German Code, and in section 20 of the Prussian Charter, “Science and her teaching shall be free!”