Page:Catholic Encyclopedia, volume 9.djvu/276

 Lzn

241

Lin

vqgeneration of damaged parts of the embiyo Is be- ooming more clearly recogxuxed every day. The trend of the best scientific thought is clearly evident in cur- rent bioloffical literature. Thus I^fessor Wilson of Columbia University in 1906 closes his admirable ex- position of the course of recent research over the whole held with the conclusion that "the study of the cell has on the whole seemed to widen rather than to nar- row the enormous gap that separates even the lowest form of life from the inorganic world " (The Cell, 4.34). In these words, however, ne is only affirming a fact to which the distinguished Oxford biologist Dr. Haldane also testifies: *'To any physiologist who candidly re- views the progress of the last mty years, it must bo perfectly evident that, so far from having advanced towards a physico-chemical explanation oflife, we are in appearance very much farther from one than we were fifty years ago. We are now more definitely aware of the obstacles to any advance in this direction, and there is not the slightest indication that they will be removed, but rather that with further increase of knowledge and more refined methods of physical and ehemicalinvestigation they will only appear more and more difficult to surmount." (Nineteenth Centurv, 1898, p. 403). In Germany Hans Driesch of Heidcl- beix is at the present day, perhaps, the most candid and courageous advocate of vitalism among German biologists of the first rank. Since 1899 he has pro- claimed his belief in the "autonomy" and "dynam- ical teleology " of the organism as a whole. The vital factor he boldly designates "entelechy", or "psy- choid", and recommends us to return to Aristotle for the most helpful conception of the principle of life. His views on some points are unfortunately and (piite unnecessarily, as it seems to us, encumbered by Kan- tian metaphysics; and he appears not to have adtv quately grasped the Aristotelian notion of entclechy as a constitutive principle of the living being. Still, he has furnished valuable contributions Imth to science and the philosophy of life.

Side by side with this vitalistic movement there continues, of course, an energetic section of represen- tatives of the old mechanical school in men like H&ckel, Loeb, Le Dantec, and Verworn, who still at- tempt physico-chemical explanations; but no new ar- guments have been adduced to jastify their claims. Many others, more cautious, aclopt the attitude of agnosticism. This position, as Reinke justly olv serves, has at least the merit of dispensing from the labour of thinking. The present neo- vitalistic reac- tion, however, as the outcome of very extensive and thorough-going research, is, we venture to think, the harbinger of a widespread return to more accurate science and a sounder philosophy in respect to this great problem. With ref^ard to the auestion of the origin of life, the whole weight of scientiuc evidence and auUiority during the past half centur\' lias gone to demonstrate with increasing cogency Harvey's axiom Omne vivena ex -vivo, that life never arises in this world save from a previous living l)eing. It claims even to have established Virchow's generalization (1858) Omnia cdlula ex cdluUiy and even Flemming's further advance (1882), Omnia nudeua e nncleo.

The history of vitalism, which we have thus briefly outlined, shows how the advance of biological re- search and the trend of the best modern scientific thought is moving steadily back in the direction of that conception of life to be found in the scholastic phiioeophy, itself based on the teaching of Aristotle. We shall now attempt a fuller positive treatment of the dodnne adopted by the great body of Catholic phi- kMophers.

II. Doctrine. — A. Science, — Life is that perfec- tion in a living beinf^ in virtue of which it is capable of self-movement or mmianent action. Motion, thus understood includes, besides change of locality, all alterations in quality or quantity, and all transition IX.— 16

from potentiality to actuality. The term is applied onl^ analogically to God, wno is exempt from even accidental modification. Self-movement of a being is that effected by a principle intrinsic to the nature of the beinff, though it may be excited or stimulated from without. Immanent action is action of which the terminus remains within the agent itself, e. g. thought, sensation, nutrition. It is contrasted with transiejxt action, of which the effect passes to a being distinct from the agent, e. g. pushing, pulling, warm- ing, et<5. Immanent activity can be the property only of a principle which is an intrinsic constituent of the agent. In contrast with the power of self-movement inertia is a fundamental attrioute of inanimate mat- ter. This can only be moved from without. There are three grades of life essentially distinct: vegetative, sentient or animal, and intellectual or spiritual life; for the capacity for immanent action is of three kinds. Vegetative operations result in the assimilation of inaterial elements into the substance of the living be- ing. In animal conscious life the vital act is a modifi- cation of the sentient organic faculty ; whilst in rational life the intellect expresses the object by a purely spir- itual modification of itself. IJfe as we know it in this world is always bound up with organized matter, that is, with a material structure consisting of orgaas, or heterogeneous parts, specialized for different func- tions and combined into a whole.

The ultimate units of which all organisms, whether plant or animal, arc composed, are minute particles of protoplasm, calle<i cells. But even in the cell there is differentiation in structural parts and in function. In other words, the cell itself living apart is an organism. The complexity of living structures varies from that of the single cell ama?ba up to the elephant or man. All higher organisms start from the fusion of two germ- cells, or gametes. When these are unecjual the smaller one — the spermatozoon — is so minute in relation to the larger, or ovum, that their fusion is commonly spoken of as the fertilization of the ovum by the si)ermatozoon. The ovum thus fertilized is endowed with the power, when placed in its appropriate nu- trient medium, of building itself up into the full-sized living being of the specific tvpe to which it belongs. Growth throughout is effected by a continuous process of cell cleavage and multiplication. The fertilized ovum undergoes certain internal changes and then di- vides into two cells juxtaposed. Each of tlie pair passes through similar changes and subdivides in the same way, forming a cluster of four like cells; then of eight; thcn>pf sixteen and so on. The specific shape and different organs of the future animal only grad- ually manifest themselves. At first the cells present the appearance of a bunch of grapes or the grains of a mulberry, the monda stage; the growth proceeds rap- idly, a cavitv forms itself inside and the blasiosphere stage is reached. Next, in the case of invertebrates, one part of the sphere invaginates or collapses inwards and the embr\'o now takes the shape of a small sac, the gastrula stage. In vertebrates instead of invagi- nation there is une<|ual growth of parts and the dfe- velopment continuing, the outlines of the nervous system, digestive cavity, viscera, heart, sense-organs, etc. ajjpear, and the specific type becomes more and more distinct, until there can lie recognized the struc ture of the particular animal — the fish, bird, or mam- mal. The entire organism, skin, bone, nerve, muscle, etc. is thus built up of cells, all derived by similar processes ultimatelv from the original germ cell. All the characteristic features of life and the formative power which constructs the whole edifice is thus jxw- scssed by this germ-cell, and the whole problem of life meets us here.

The chief phenomena of life can l>e seen in their simplest form in a unicellular organism, such as the amoeba. This is visible under the microsco|)e as a minute speck of transparent jelly-like 5^ti^^Q\\'dSK^«