ART. XLVIII.-On Spontaneous Generation.

1. Remarks of Prof. MILNE EDWARDS on the value of certain facts as evidence of the spontaneous generation of animals, made before the Academy of Sciences at Paris,* at the session of January 3, 1859.

Physiologists have long been divided on the subject of the origin of life in organized beings. The larger part believe that this force exists only where it has been transmitted; that from the creation of the species till the present time, an uninterrupted chain of possessors of this power has communicated it successively; and that dead matter has no power of organizing a plant or an animal unless it be submitted to the action of a living being or a germ that has proceeded from an individual of some species.

Others, on the contrary, have held that inert matter, under certain chemical and physical conditions, could take on life with out the agency of a generating being; that plants and animals may produce themselves in all their parts without deriving the principle of existence from another living body; and that consequently life itself must be considered, not as a force which has been imparted peculiarly to organized beings, but as a general property of organizable matter manifesting itself under certain favorable conditions.

In my lectures and writings, I have often combatted this last doctrine; and the hypothesis of spontaneous generation has to-day so few supporters among zoologists, that I should have feared to abuse the patience of the Academy in discussing it at this time, had I not seen in the Report of a recent session of this body, that one of our correspondents, Mr. Pouchet, had made it the object of new researches and had arrived at conclusions, which, if right, sustain the idea that living beings may be made by the same general forces on which chemical combinations in inorganic nature depend. Since reading this memoir, I have thought it might be useful to submit to the judgment of my colleagues my reasons for rejecting its conclusions; and it ap pears to me desirable also to know the opinions of other physiologists on a point of so much importance: besides, the question reaches beyond the domain of the natural sciences, and we may look for additional light from our chemists.

Long before the invention of the microscope had enabled zoologists to discover the animalcules which are produced in

* Comptes Rendus, 1859, p. 23. The Zoologists and other members of the Academy who have here expressed their views on spontaneous generation, are at the head of their respective sciences in France.

SECOND SERIES, VOL. XXVII, No. 81.-MAY, 1859.

myriads in waters containing an infusion of organic matters, it had been observed that dead bodies when left to putrefy often became populated with swarms of life; and as the intervention of no living being was manifest in their production, the old naturalists supposed them a product of the putrefaction which was in progress, believing that the material, after ceasing to pertain to a living being, could reorganize itself under a new form and so constitute animals which had no parent; accordingly, that life is not the cause, but the consequence of a certain mode of arrangement of the molecules composing these substances, and that this kind of molecular grouping could be determined by inorganic forces in nature.

The occurrence of maggots in carrion was one of the cases. But since the study of the origin of these animals by the Florentine Academy, happily named "del Cimento," and the exact investigations of Redi, one of its members, it has been well understood that these worms about dead bodies, far from being a result of spontaneous generation, are the brood of well known. insects, species which find in such bodies the conditions requisite for development, and hence, through a marvellous instinct, deposit there their eggs.

The experiments of Redi, which date from the middle of the 17th century, left no uncertainty respecting these larves. But while very easy to establish the fact respecting animals as large as flies, it was far less so with regard to infusory animalcules, which are discernible only by means of the microscope, and whose germs are so excessively minute that they have escaped all the methods of observation which the science of optics has supplied. When, therefore, Lewenhoek and his successors made known the existence of these animalcules, the hypothesis of spontaneous generation regained favor. While some physiologists regarded them as derived from germs of extreme minuteness which were spread every where in nature, and floating as fine dust in the atmosphere, settled on all bodies to develop only where the conditions of air, water and organic decomposition favored; others denied the existence of germs, and supposed that under the dissolving action of the water, the dead organic substance took on life and so came out as new beings.

Analogy afforded a strong argument for the first of these opinions. The second has often been sustained by appeals to researches claiming that animalcules were produced under circumstances in which all germs from external sources were excluded, and all present in the waters used had been destroyed. Frey and several other observers have thought that they had succeeded in securing these conditions and still had found their infusions populated with microscopic plants and animals; whence the conclusion that these organisms were a result of spontaneous generation.

It does not pertain to me to pronounce on the origin of microscopic plants, for this difficult subject must be left to botanists. But as regards animals, I do not hesitate to say that the experimental conditions required to prove the truth of spontaneous generation have not been realized by any of the predecessors of Mr. Pouchet. And are the researches of this naturalist, that have recently been communicated to the Academy, free from the objections which are made against earlier experiments? I believe not: and before mentioning some observations I have had occasion to make on this subject, I will briefly state the reasons that lead me to this conclusion.

I do not question the facts stated by Mr. Pouchet. The point is, Have these facts the significance attributed to them? I believe not. His experiment is briefly as follows. After having boiled some water and kept the liquid from contact with the air, he puts it into contact with pure oxygen, and introduces a certain quantity of hay, which had been previously enclosed in a flask and heated for a half hour in a stove whose heat was car ried up to 100° C. or to the boiling point of water. The infusion thus prepared was hermetically sealed, and after some days Mr. Pouchet found infusoria developed in it.*

To make these facts sure proof that the animalcules obtained were not derived from the hay put into the infusion, it must be shown that the heat of the stove had destroyed all the germs. Mr. Pouchet presumes that this is true, because on boiling in water the spores of a Penecillum he has seen that they were decomposed. But this reason does not satisfy me.

In the first place, was the hay, although enclosed in a flask and kept thirty minutes in a stove at 100° C. (212° F.), really carried up to the temperature of boiling water? Mr. Pouchet believes it; but I think to the contrary, and I think that physicists and chemists will judge so too. The equilibrium of temperature under such conditions is not established so promptly as this; it appears to me probable that the hay, enclosed in a glass vessel and surrounded by air in repose, both substances bad conductors of heat, was in reality heated but little by the heat of the stove during the short time it was exposed to it.

But supposing that the hay was heated up to 100° C., can we then conclude that the germs had lost their vitality and were incapable of development? No, for there is an important distinction here to be recognized between the action of heat on organized bodies which contain water and on those which are in the dry

state.

This follows directly from the researches, already old, of our learned colleague, Mr. Chevreul. Although in ordinary cir cumstances death takes place when animals are exposed to a

* See page 253 of this volume.

temperature sufficient to determine the coagulation of the hy drated albumen in their tissues, we know that this is not always so in the case of those which have been previously dried. In fact, fifteen years since, Mr. Doyère made known that certain animalcules, such as the Tardigrades,* after being sufficiently dried would preserve their vitality for several hours while exposed in a stove whose temperature is much higher than that used by Mr. Pouchet for his flask of hay. I have seen these animalcules resist thus the very prolonged action of a stove whose temperature stood at 120° Centigrade (248° F.); and in the researches of Mr. Doyère, the heat of the ambiant medium was carried to 140° C. (284° F.) without death ensuing from the heat.

What is true for the Tardigrades, animals of a very complex structure, may also be true for the germs of Infusoria in general; and I conclude that nothing in the trials of Mr. Pouchet authorizes us to infer that the germs of the animalcules obtained by this naturalist were not in the hay that was used in his experiment. I will even say that the experiments of our correspondent do not seem to me to add any new probability in favor of the hypothesis of spontaneous generation.

I have often made analogous experiments; and I have always found that the living animalcules which appeared in water containing dead organic matters, were increasingly rare the more complete the precautions employed for protecting the liquids from the introduction of germs. In more than one trial, I should have believed that spontaneous generation had taken place under my own eye, had I not, on reflecting on the conditions under which I was operating, perceived sources of error, and on setting these aside, observed negative results to multiply. I will not occupy the Academy with the general recital of these trials, but will ask permission to recount briefly a single series of experiments in which some infusions, that if exposed to the air would in all probability have given birth to animalcules, afforded none when the imprisoned matters in the hermetically sealed vessel had been subjected to a temperature high enough to cause the coagulation of the contained albuminoid substances.

I placed in two tubes, having the form of test-tubes, the water and the organic matters for the trial. One of these tubes, which was two-thirds filled with air, was then closed by means of a lamp, and both this and the other tube were then plunged into a bath of boiling water. The bath was kept in ebullition long enough to establish an equilibrium between the water outside

The Tardigrade animalcules are minute worm-shape animals about a fortieth of an inch in length, belonging to the Rotatoria of Ehrenberg, and therefore much higher in structure than the ordinary Infusoria,

and the liquid of the two infusions; and then the tubes were allowed to cool and left to themselves, care being taken to examine the contents from time to time. After some days, I found animalcules in the tube which remained open to the atmosphere, but not a single one in that which had been hermetically sealed.

I have been accustomed to cite these experiments in my lectures, but had not thought of bringing them before the Academy, because negative results acquire importance only when they have been obtained constantly in a large number of trials, and also because the spontaneous generation of animals appears to me so little probable that I would not devote time to the repetition of researches on a subject which seems to be already settled. Only in view of the communication of our correspondent, and the interest that experimenting in this direction may excite in our young physiologists, have I been induced to bring out these facts among the reasons for still rejecting the hypothesis of spontaneous generation as an explanation of facts connected with the multiplication of animalcules.

An hypothesis which is not necessary in order to understand the phenomena made known by observations, and which is in flagrant discordance with all that analogy teaches us, seems to have no right to a place in science. It may be that chemistry will be able to make all the kinds of substances which occur in the constitution of living bodies; but as to the genesis of living organisms without the concurrence of vital force, I see no reason for believing it. Until more amply instructed, I shall therefore continue to think that in the animal kingdom there is no such thing as spontaneous generation, and that all animals, large and small, are subject to the same law, and can exist only when they have been generated by living beings.

2. Remarks on the same occasion, by Mr. PAYEN, Professor in the Conservatoire Imperial des Arts et Metiers.

Some time in 1843, there occurred an alteration of the bread at Paris by a rapid growth of cryptogamic vegetation; and after having determined in connection with Mr. Mirbel the cause of the phenomenon, which had produced some excited dissatisfaction among the people, I endeavored to determine the temperature at which the sporules of the Oidium aurantiacum lost their germinative power. These sporules were heated at first for an hour to 100° C. (212° F.) in a tube inserted in an oil-bath. A part were then withdrawn and exposed in the proper circumstances for growth; and germination took place. The remainder of the sporules were then heated to 120° C.; and they neither underwent change of color nor lost their property of germination. Finally, they were heated to 140° C., when their appearance