statements made by an anonymous writer who had shown himself little worthy of being heard upon the subjects in dispute. Spallanzani on this occasion very wisely said* :—“When it is a question concerning observations and experiments, it is necessary to have repeated them with much circumspection before venturing to pronounce that they are doubtful or untrustworthy. He who will allow himself to speak of them with contempt, and who can only attempt to refute them with writings composed by the glimmer derived from a treacherous lamp, will not find himself in a condition to retain the esteem of learned men." The anonymous writer (in his 'Lettres à un Américain'), to whom Spallanzani referred, had gone so far as to doubt the statements of Needham as to the constant appearance of organisms in infusions which had been previously boiled, and also intimated that even if they were to be found, it was only because they had been enabled to resist the destructive influence of the boiling fluid. This latter assertion was emphatically denied by Spallanzani, his denial being based upon a most extensive series of experiments with eggs in great variety and with seeds of all degrees of hardness; these were all found to be killed by a very short contact with boiling water. Spallanzani had thoroughly satisfied

* Loc. cit., p. 114.

himself that even very thick-coated seeds could not resist this destructive agent; whilst he thought that the idea, entertained by some, of the eggs of the lowest infusoria being protected from the injurious influence of the boiling water by reason of their extreme minuteness, was a supposition so improbable as scarcely to deserve serious consideration. Such a notion was, he thought, wholly opposed to what was known concerning the transmission of heat. Whilst, therefore, the opinion of those who believe that eggs have the power of resisting the destructive influence of boiling water could be fully refuted, Spallanzani thought it by no means followed that the infusoria which always, after a very short time, appeared in boiling infusions had arisen independently of the existence of eggs. The infusions being freely exposed to the air, it was very possible that this air had introduced eggs into the fluids, which by their development had given birth to the infusoria.*

After the lapse of a century it has at last been clearly shown that this supposition of aërial con

* A few pages further on this view is thus shortly expressed :- -" Il est évident que touts les tentatives faites avec le feu, peuvent bien servir à prouver que les animaux microscopiques ne naissent point des œufs que l'on supposait exister dans les infusions avant qu'on leur fit sentir le feu; mais cela n'empêche pas qu'ils n'aient pu être formés de ceux qui auront été portés dans les vases après l'ébullition."

G

processes of putrefaction,

tamination advanced by Spallanzani (warrantable and natural as it was at the time) is one which, in the great majority of cases, is devoid of all foundation in fact, so far as concerns the organisms essentially associated with viz. Bacteria and Vibriones. The means of proving this statement based upon independent observations made by Professor Burdon Sanderson and myself, were recently submitted to the consideration of the Royal Society.† Before the reading of this communication I was under the impression that almost everyone of those who had taken part in the controversies which had been carried on both here and abroad concerning the Origin of Life were prepared to admit, as Spallanzani had done, that the eggs or germs of such organisms as appear in infusions were unable to survive when the infusions containing them were raised to the temperature at which water boils. This impression was produced in part by the explicit statements on this subject that had been made by very many biologists, and also in part by a comparatively recent and authoritative confirmation which this view as to the destructive effects of boiling infusions upon Bacteria had received. Little more than two years ago Professor Huxley, as President of the British

*

See Proceedings of Royal Society, No. 141, 1873, p. 129.

Association for the for the Advancement of Science® recorded experiments in his Inaugural Address which were obviously based upon this belief as a starting-point; and subsequently, in one of the Sectional Meetings, after referring to some of my experiments, and to the fact that all unmistakeably vital movements ceased after Bacteria had been boiled, Professor Huxley added* :-"I cannot be certain about other persons, but I am of opinion that observers who have supposed that they have found Bacteria surviving after boiling have made the mistake which I should have done at one time, and, in fact, have confused the Brownian movements with true living movements." Some eminent biologists do not now (in reference to the experiments cited in my last communication) suggest that the organisms found in the infusions were dead and had been there before the fluids were boiled: they express doubts concerning that which seems formerly to have been regarded as established, and now wish for evidence to show that the germs of Bacteria and Vibriones are killed in a boiling infusion of hay or turnip, as they have been proved to be in Pasteur's Solution' and in solutions containing ammonic tartrate and sodic phosphate.

With the view of removing this last source of * See Report in Quart. Journ. of Microscop. Science, Oct. 1870.

doubt more effectually, and also of refuting the unwarrantable conclusion* of M. Pasteur, to the effect that the germs of Bacteria and Vibriones are not killed in neutral or slightly alkaline fluids at a temperature of 212° F., I almost immediately after the reading of my last communication commenced a fresh series of experiments.

Nearly two years ago, in my 'Modes of Origin of Lowest Organisms,' I brought forward evidence to show that Bacteria, Vibriones, and their supposed germs are killed at a temperature of 140° F. (60°C.) in neutral or very faintly acid solutions containing ammonic. tartrate and sodic phosphate, and also evidence tending to show that these living units were killed in neutral infusions of hay and in acid infusions of turnip at the same temperature. The crucial evidence adduced concerning the degree of heat destructive to Bacteria, Vibriones, and their germs, in the saline solution, was of this nature. The solution had been shown to be incapable of engendering Bacteria and Vibriones (under all ordinary conditions) after it had been boiled, although it still continued capable of supporting the life and

* Reasons for this opinion have been fully set forth in "The Beginnings of Life," vol. i., pp. 374 et seq.; or the discriminating reader may at once find my justification for this expression by reading pp. 58–66, of M. Pasteur's memoir in "Ann. de Chim. et de Physique," 1862.