from decayed wood, herbs, and fruits. But God is the Creator of all things. It may therefore be said that those animals which spring from the bodies, and especially the corpses of other living beings were only created with them, potentialiter and materialiter. But of those which spring from the earth, or the water, we may unhesitatingly say that they were created on the fifth and sixth days." This passage from S. Augustine was included in the great dogmatic compendium of the Middle Ages, the Sentences of Peter Lombard, and the schoolmen maintained this view. S. Thomas,1 no doubt, protests against Avicenna's theory that all animals could spring without seed from a certain intermixture of the elements, but he does not dispute the fact that certain animals spring from putrefied plants and animals.

The Fathers and the schoolmen did not derive this theory from the Bible, but as it was not opposed to the Bible they took it quite naturally from the ancient scientific writers, especially from Aristotle. We know that they not only assert that midges, fleas, lice, and other vermin sprang simply from the earth, but also frogs, serpents, and mice; the eel also, in which Aristotle could find no ovary, was supposed to have originated from slime. Even in the seventeenth century, the learned Jesuit, Athanasius Kircher, gives regular receipts for bringing animals into existence : "Take as many serpents as you like, dry them, cut them into small pieces, bury these in damp earth, water them freely with rain-water, and leave the rest to the spring sun. After eight days the whole will turn into 1 Q. 71, a. 1; q. 72, a. 1.

little worms, which, fed with milk and earth, will at length become perfect serpents, and by procreation will multiply ad infinitum."1

You see that theologians made no objection to the generatio æquivoca when it was assumed to a far greater extent than is ever the case now-a-days; and we need therefore certainly not dispute the principle of spontaneous generation from a theological point of view. If organic beings really spring from inorganic matter, we must simply suppose, with S. Augustine,2 that God created some substances with the faculty of bringing forth certain classes of plants or animals according to the natural laws given by Him, and under certain conditions foreseen by Him from all eternity. No theologian-and, I think, no philosopher -ought to assert the impossibility of spontaneous generation. The fact that we do not understand how organic beings can spring from inorganic matter, is no proof that it cannot happen; we do not understand many physiological events which undoubtedly occur." The question whether spontaneous generation takes place among certain classes of plants and animals, is one which can be decided only by means of observation. And the classes of organic beings, among which it was thought that spontaneous generation might exist, have become fewer and fewer under continuous observation, especially since the end of the seventeenth century.

The well-known saying, Omne vivum ex ovo, proceeds from the English savant Harvey, who is famous as the

1

Quenstedt, Sonst und Jetzt, p. 229. 3 Martin, Les Sciences, p. 94.

2

Aug. De Trin. iii. 9.

discoverer of the circulation of the blood. But Harvey did not mean by this saying what is now generally understood; he only meant to assert that every living being originated in a small spheroidal portion of organic matter. He did not deny that such an egg could spring from inorganic matter by spontaneous generation. In his time, for instance, it was commonly believed that insects could spring from putrefied plants and animals. If a piece of flesh is placed in the sun and allowed to putrefy, maggots will appear in it, from which will proceed insects; and these maggots were generally believed, in the seventeenth century, to have come into existence by spontaneous generation. It was the Italian savant Redi who refuted this theory, in a very simple way, about 1690. He covered the piece of flesh with a very fine gauze, and then exposed it to the same influence; the result was that no maggots and insects were generated, and it was proved that the maggots in the uncovered piece of flesh proceeded from insects which came to lay their eggs in it, and the eggs were then hatched by the heat of the sun.1

The opinion that the so-called entozoa, intestinal worms and such like, originated by spontaneous generation from unhealthy juices in the bodies of men or animals, lasted longer. The extraordinary wanderings and changes of these parasites have only been detected in this century, principally by Van Beneden, and several German savants, Von Siebold, Küchenmeister, Leuckart, and others. There is no doubt that they do not originate by spontaneous generation, but

1

Huxley, On our Knowledge of the Causes and Phenomena of Organic Nature, p. 73.

are reproduced like other animals, principally from eggs.

Further, it was formerly assumed that the so-called mould fungi originated by spontaneous generation from germs which were, as it were, crystallized out of mouldy bodies, as the organized produce of decomposition. This opinion also is erroneous; at least A. de Bary says, "Hitherto we know of no demonstrated fact which would establish this theory; it rather appears, from many experiments made with great care, that the mould fungi in no way differ from other fungi with reference to their origin." Neither do the so-called yeast fungi or ferment cells afford any proof of spontaneous generation. Yeast consists of very small vegetable cells, which, when they are placed in a liquid susceptible to the action, multiply by budding, and produce fermentation. The opinion that these cells originated by parentless spontaneous generation may be treated in the same way as that of the supposed spontaneous generation of mould fungi.3

2

A bitter controversy has been going on in France in recent years (since 1818), especially between the Academician Pouchet (ob. 1872) and Pasteur, about the so-called infusoria; the Abate Spallanzani in the last century, and in our century Ehrenberg, Balbiani, and others, having denied that they originate by

1 Cf. C. O. Weber, Ueber die Entstehung der Eingeweidenwürmer, in the Proceedings of the Association of Natural History, Bonn 1863, xx. 95. M. Pertz, Ueber den Parasitismus in der organischen Natur, Berlin 1869, p. 18. Quenstedt, Sonst und Jetzt, p. 231. Natur und Offenbarung, 1864, p. 315.

2 Veber Schimmel und Hefe, Berlin 1869, p. 56.

3 A. de Bary, Op. cit. p. 60. F. Hoppe-Seyler, l'eber die Quellen der Lebenskräfte, Berlin 1871, p. 15, 20 seq. F. Cohn, Ueber Bakterien die kleinsten lebenden Wesen, Berlin 1872, p. 18.

Pouchet maintained that

spontaneous generation. small microscopic organic beings- they are called bacteria, and it is still uncertain whether they are plants or animals-originated by spontaneous generation if water was poured on to an organic substance, for instance, hay. Pasteur explained the appearance of these animals, by the precipitation of small germs which were floating in the air; and in order to substantiate this statement, he quoted the results of a series of ingenious experiments. He killed all the organic germs which were contained in the fluid with which he experimented, by boiling it; and then he either entirely stopped the access of air, or took precautions to ensure that all the organic germs contained in the air which he admitted should be killed,-for instance, by admitting the air through a red-hot tube, -or that they should be caught in cotton wool. In all these cases, no organic life was developed in the fluid.1

Many scientific men think that the doctrine of the

1 "Pasteur fixed in the window of his room a glass tube, in the centre of which he had placed a ball of gun-cotton; . . . one end of the glass tube was, of course, open to the external air; and at the other end of it he placed an aspirator, a contrivance for causing a current of the external air to pass through the tube. He kept this apparatus going for four-andtwenty hours, and the result was, that a very fine dust was gradually deposited at the bottom of it. That dust, on being transferred to the stage of a microscope, was found to contain an enormous number of starch grains. . . . But besides these, Pasteur found also an immense number of other organic substances, such as spores of fungi, which had been floating about in the air, and had got caged in this way. Pasteur also took one of these vessels of infusion, which had been kept eighteen months without the least appearance of life, and, by a most ingenious contrivance, he managed to break it open and introduce such a ball of gun-cotton, without allowing the infusion or the cotton ball to come into contact with any air but that which had been subjected to a red heat; and in twentyfour hours he had the satisfaction of finding all the indications of what had been hitherto called spontaneous generation. . . . He then took some decaying animal or vegetable substance, . . . and filled a vessel