Vickipedia

GENERATION, SPONTANEOUS. From the earliest period to the termination of the middle ages, no one called in question the doctrine that, under certain favorable conditions, of which putrefaction was one of the most important, animals might be produced without parents. Anaximander and Empedocles attributed to this form of generation all the living beings which first peopled the globe. Aristotle, without committing himself to so general a view, maintains that animals are sometimes formed in putrefying soil, sometimes in plants, and sometimes in the fluids of other animals, and lays down the following general principle, ‘ that every dry substance which becomes moist, and every moist body which is dried, produces living creatures, provided it is fit for nourishing them.’ The views of Lucretius on this subject are shown in the following lines :

Nonne vides quæcunque morâ, fluidoqne liquore
Corpora tabuerint, in parva animalia verti?

And Pliny maintains that ‘ quædam gignuntur ex non genitis, et sine ullâ simili origine.’ Virgil’s directions for the production of bees are known to every reader of the Georgics, and an expression in the Book of Judges (xiv. 14) probably points to a similar opinion.

Passing from classical times to the later period of the middle ages, and the two succeeding centuries, we may quote amongst the advocates of this theory Cardan—who, in his treatise De Subtilitate (1542), asserts that water engenders fishes, and that manyanimals spring from fermentation—Aldrovandus, Licetus, Gassendi, Scaliger, Van Helmont, who gives special instruction for the artificial production of mice, and Kircher, who in his Mundus Subterraneus (in the chapter ‘ De Panspermia Rerum ‘) describes, and actually figures, certain animals which were produced under his own eyes by the transforming influence of water on fragments of the stems of different plants !

Redi, the celebrated Italian naturalist, whose Experiments on the Generation of Insects were published in 1668, seems to have been the first opponent that the doctrine of spontaneous generation encountered. In this work, he proves that the worms and insects which appear in decaying substances are in reality developed from eggs, deposited in those substances by the parents. Leuwenhoek, Vallisneri, Swammerdam, and other eminent naturalists, soon contributed additional facts and arguments in favor of Redi’s view; and as from the time of Redi to the present day, the tide of opinion has generally turned strongly against the doctrine in question, it is unnecessary to carry the historical sketch further.

The entozoa, however, continued to be a great stumbling-block. ‘ When,’ says Professor Owen, ‘ the entozoologist contemplated the tænia fixed to the intestine, with its uncinated and suctorious head buried in the mucous membrane, rooted to the spot, and imbibing nourishment like a plant—when he saw the sluggish distoma (or fluke) adhering by its sucker to the serous membrane of a close internal cavity, he naturally asked himself how they got there; and finding no obvious solution to the difficulty of the transit on the part of such animals, he was driven to the hypothesis of spontaneous generation to solve the difficulty. It is no wonder that Radolphi (1808) and Bremser (1824) who studied the entozoa rather as naturalists than physiologists, should have been led to apply to them the easy explanation which Aristotle had given for the coming into being of ail kinds of Vermes—viz., that they were spontaneously generated. No other explanation, in the then state of the knowledge of the development of the entozoa, appeared to be adequate to account for the fact of their getting into the interior cavities and tissues of higher animals.’ The recent investigations of Von Siebold, Kuchenmeister, Van Beneden,Philippi, &c., regarding the development and metamorphoses of the entozoa, have, however, tended to remove nearly all the difficulties which this subject presented; and the advocates of spontaneous generation are fairly driven from this, one of the last of their battle-fields.

The only point at present in dispute is, whether microscopic organisms (animals or plants) may be spontaneously generated. It is well known that if we examine under the microscope a drop of water in which almost any animal or vegetable substances have been infused, and which contains the particles of such substances in a state of decay or decomposition, it is found to swarm with minute living organisms. The question at issue is this : Are these organisms developed in the water, if the necessary precautions have been taken to exclude every animalcule or germ capable of development both from the water and from the air that has access to it ? A well-known experiment, devised by Professor Schulze of Berlin (a description of which may be found in Owen’s Lectures on the Invertebrate Animals, 2d ed. p. 44), shows that with due precautions in reference to these points, no animal or vegetable organisms are produced.

This experiment was continued uninterruptedly from the 28th of May until the beginning of August, ‘ and when, at last, the professor separated the different parts of the apparatus, he could not find in the whole liquid the slightest trace of infusoria or con-fervæ, or of mould; but all three presented themselves in great abundance a few days after he had left the flask standing open.’ A vessel with a similar infusion, which he placed near the apparatus, contained vibriones and monads on the second day of the experiment, to which were soon added larger polygastric infusoria.

A few years ago, M. Pouchet announced that he had repeated Schulze’s experiment with every precaution, but that animalcules and plants were invariably developed in the infusion on which he operated. To prove that the atmospheric air contained no germs, he substituted artificial air—that is to say, a mixture of 21 parts of oxygen gas with 79 of nitrogen. The air was introduced into a flask containing an infusion of hay, prepared with distilled water and hay that had been exposed for twenty minutes to a temperature of 212°. He thus apparently guarded against the presence of any germs or animalcules in the infusion or in the air. The whole was then hermetically sealed, so that no other air could gain access; yet after all these precautions, minute animal and vegetable organisms appeared in the infusion. He repeated the experiment with pure oxygen gas instead of air, and obtained similar results. These experiments are described by Pouchet in the Annales des Sciences Naturelles (1858, 4th series, vol. ix. p. 372), and the same volume contains important articles by Milne Edwards, and by De Quatrefages, in opposition to Pouchet’s views.

A very large majority of our physiologists of the present day reject the doctrine; most of the apparently exceptional cases, as, for example, the mysterious presence of the entozoa, have been found to admit of ready explanation; and if we do not positively deny the possibility that animalcules may be generated spontaneously, we may at all events assert that such a mode of generation is not probable, and has certainly not been proved to exist. Haeckel in Germany and Bastian in England may be named as confident defenders of the doctrine of Abiogenesis, as spontaneous or equivocal generation is now technically termed. Those who wish to know fully the arguments for and against the doctrine, are referred, on the one hand, to Pouchet’s He’terogenie, ou Traite de la Ge”ne”ration Spontanee (1859), and to Bastian’s Beginnings of Life (1872); on the other, to Pasteur’s Examen de la Doctrine det Generations Spontanees • and to the admirable statement, expository and historical, in Huxley’s Critiques and Addresses (1878).