Читать книгу Form and Function - E. S. Russell - Страница 14

Science, in so far as it rises above the mere accumulation of facts, is a product of the mind's creative activity. Scientific theories are not so much formulæ extracted from experience as intuitions imposed upon experience. So it was that Goethe, who was little more than a dilettante,[70] seized upon the essential principles of a morphology some years before that morphology was accepted by the workers.

Goethe is important in the history of morphological method because he was the first to bring to clear consciousness and to express in definite terms the idea on which comparative anatomy before him was based, the idea of the unity of plan. We have seen that this idea was familiar to Aristotle and that it was recognised implicitly by all who after him studied structure comparatively. In Goethe's time the idea had become ripe for expression. It was used as a guiding principle in Goethe's youth particularly by Vicq d'Azyr and by Camper. The former (1748–1794), who discovered[71] in the same year as Goethe (1784) the intermaxillary bone in man, pointed out the homology in structure between the fore limb and the hind limb, and interpreted certain rudimentary bones, the intermaxillaries and rudimentary clavicles, in the light of the theory that Vertebrates are built upon one single plan of structure.

"Nature seems to operate always according to an original and general plan, from which she departs with regret and whose traces we come across everywhere" (Vicq d'Azyr, quoted by Flourens, Mém. Acad. Sci., XXIII., p. xxxvi.).

Peter Camper (1722–1789), we are told by Goethe himself in his Ostéologie, was convinced of the unity of plan holding throughout Vertebrates; he compared in particular the brain of fishes with the brain of man.

The idea of the unity of plan had not yet become limited and defined as a strictly scientific theory; it was an idea common to philosophy, to ordinary thought, and to anatomical science. We find it expressed by Herder (who perhaps got it from Kant) in his Ideen zur Philosophie der Geschichte der Menschheit (1784), and it is possible that Goethe became impressed with the importance of the idea through his conversations with Herder. Be that as it may, it is certain that Goethe sought for the intermaxillaries in man only because he was firmly convinced that the skeleton in all the higher animals was built upon one common plan and that accordingly bones such as the intermaxillaries, found well developed in some animals, must also be found in man. The idea was not drawn from the facts, but the facts were interpreted and even sought for in the light of the idea. "I eagerly worked upon a general osteological scheme, and had accordingly to assume that all the separate parts of the structure, in detail as in the whole, must be discoverable in all animals, because on this supposition is built the already long begun science of comparative anatomy."[72]

The principle comes to clear expression in his Erster Entwurf einer allgemeinen Einleitung in die vergleichende Anatomie (1795).[73] He writes:—"On this account an attempt is here made to arrive at an anatomical type, a general picture in which the forms of all animals are contained in potentia, and by means of which we can describe each animal in an invariable order."[74] His aim is to discover a general scheme of the constant in organic parts, a scheme into which all animals will fit equally well, and no animal better than the rest. When we remember that the type to which anatomists before him had, consciously or unconsciously, referred all other structure was man himself, we see that in seeking after an abstract generalised type Goethe was reaching out to a new conception. The fact that only the structure of man and the higher animals was at all well-known in his time led Goethe to think that his general Typus would hold for the lower animals as well, though it was to be arrived at primarily from a study of the higher animals. All he could assert of the entire animal kingdom was that all animals agreed in having a head, a middle part, and an end part, with their characteristic organs, and that accordingly they might, in this respect at least, be reduced to one common Typus. Goethe's knowledge of the lower animals was not extensive.

Though Goethe did not work out a criterion of the homology of parts with any great clearness, he had an inkling of the principle later developed by E. Geoffroy St. Hilaire, and called by him the "Principle of Connections." According to this principle, the homology of a part is determined by its position relative to other parts. Goethe expresses it thus:—"On the other hand the most constant factor is the position in which the bone is invariably found, and the function to which it is adapted in the organic edifice."[75] But from this sentence it is not clear that Goethe understood the principle as one of form independent of function, for he seems to consider that the homology of an organ is partly determined by the function which it performs for the whole. He wavers between the purely formal or morphological interpretation of the principle of connections and the functional. We find him in the additions to the Entwurf (1796), saying:—"We must take into consideration not merely the spatial relations of the parts, but also their living reciprocal influence, their dependence upon and action on one another."[76] But in seeking for the intermaxillary bone in man he was guided by its position relative to the maxillaries—it must be the bone between the anterior ends of the maxillaries, a bone whose limits are indicated in the adult only by surface grooves.

As a matter of fact Goethe's morphological views are neither very clearly expressed nor very consistent. This comes out in his treatment of the relation between structure and function. Sometimes he takes the view that structure determines function. "The parts of the animal," he writes, "their reciprocal forms, their relations, their particular properties determine the life and habits of the creature."[77] We are not to explain, he says, the tusks of the Babirussa by their possible use, but we must ask how it comes to have tusks. In the same way we must not suppose that a bull has horns in order to gore, but we must investigate the process by which it comes to have horns to gore with. This is the rigorous morphological view. On the other hand he admits elsewhere that function may influence form. Apparently he did not work out his ideas on this point to logical clearness, and Rádl[78] is probably correct in saying that the following quotation with its double assertion represents most nearly Goethe's position:—