II. To the second subclass belong fluids which, after exposure to a temperature of 212° F. or higher, may be kept clear or apparently unaltered so long as they are shut off from contact with unheated atmospheric or other organic particles, but which do undergo putrefaction, or more or less marked fermentation, soon after they are brought into contact even with mere not-living organic matter.

The experiments recorded in this communication have most conclusively proved the efficacy of notliving organic matter as a ferment or inciter of change in previously barren fluids. And combining the knowledge derived from these experiments with that which we now possess concerning the absence of living Bacteria, Vibriones, and their germs in the air, together with the known prevalence of minute organic particles and fragments of various kinds, the explanation of M. Pasteur's celebrated experiments in which.

established that living organisms could appear in saline solutions free from traces of organic impurity. Mr. Hartley did attempt to work with approximately pure saline solutions, and in other respects also the conditions of his experiments differed so much from mine, that the results which he obtained could not possibly be considered to disprove what I had previously stated. Some of his flasks were heated to 180° C., a temperature about which I had said nothing; and whilst his organic infusions were too weak, some of his saline solutions were too concentrated, though the strengths of others were not given at all. Fluids were also employed (such as urine, heated to 130° C.) which I had not made use of, and which I should not have thought of experimenting with.

he had recourse to an "ensemencement des poussières qui existent en suspension dans l'air," becomes quite easy and legitimate without having recourse to the hypothesis of Panspermism.* Now, also, are we enabled to understand all the apparent inconsistencies of those experiments in which previously boiled fluids have been exposed to the ordinary air of different localities, and have then been resealed. If many specimens of these fluids remained unchanged, whilst others, after a few days, swarmed with Bacteria and Vibriones, we may now very safely attribute these previously puzzling results to the comparative absence or presence of organic fragments in the particular volumes of air which chanced to get into the flasks, and to the different nature of the fluids employed by different experimenters.†

Many of the fluids which habitually remain clear after a previous ebullition in flasks whose necks have been plugged with cotton-wool, many times bent, or hermetically sealed after the entry of calcined air, or when enclosed in vessels which are completely full (in Gruithuisen's fashion), belong to this subclass. In

*

See the experiments before alluded to, which are recorded in chaps. iv. and v. of his Memoir.

See M. Pasteur's Memoir, chap. vii., and also Compt. Rend., Nov. 5, 1860. See also a record of other experiments made with the air of alpine regions by MM. Pouchet, Joly, and Musset, in Compt. Rend., Sept. 21, 1863.

other cases, however (as in many of those instances where urine or hay- or turnip-infusions have been employed), those who do not content themselves with a mere naked-eye inspection of the apparently pure fluids would find on microscopical examination of the sediment that such fluids were to a low degree selffermentable-that they correspond, in fact, with group E of the last subclass; whilst, in addition, my researches have shown that many of such fluids are capable of being rendered self-fermentable to a marked degree, if, instead of subjecting them to contact with calcined air or variously filtered air, its reflux after ebullition is altogether prevented by hermetically sealing the neck of the flask during ebullition. Operating in this way, I have repeatedly found that fluids freed from the pressure of air and from its influence altogether, become to a marked extent selffermentable, although the same fluids exposed to filtered or calcined air under ordinary atmospheric pressure remain unaltered and barren, or at most exhibit the very low degree of fermentability referred

* Other fluids richer in organic matter or otherwise more favourably endowed, instead of presenting this low degree of self-fermentability, are notably prone to undergo change when we attempt to preserve them in the manner described, although such modes of preparation do suffice for preserving so many fluids. This has been fully admitted by Schroeder and Dusch, Schwann, Pasteur, and others.

to as characterizing group E.* But just as amongst the self-fermentable fluids we find there are some which only engender Torula or other allied fungusgerms, so now we find that some previously boiled fluids, even when fully exposed to the air, swarm only with Torula. Those exciting agents derived from the atmosphere which, with one set of fluids, initiate changes leading to the evolution of Bacteria, with another set lead only to the evolution of Torulæ. And whilst telling us that the Bacteria which appear in previously barren fluids after exposure to air are not due to their contamination with germs of Bacteria, some observers would have us conclude that the Torulæ which appear in other previously barren fluids after a similar exposure are the products of preexisting aërial germs of such organisms. This conclusion, however, cannot readily be accepted in the face of the evidence derived from the closed-flask experiments with selffermentable fluids of the lowest degree.† Such experiments, in fact, render the hypothesis as to the widespread distribution of aërial germs of Torula wholly unnecessary, by showing that certain fluids, by reason

In illustration of this statement see "The Beginnings of Life," Appendix C, Exps. viii., ix., xiv., xv., xviii., xx., xxvi., xxx., xxxiii., and xxxvi.

+ The only evidence in favour of such a conclusion is not one jot more conclusive than that which was formerly adduced in favour of the universal prevalence of Bacteria-germs in the air.

of certain intrinsic peculiarities, when they undergo fermentation give rise to Torula only. We are thus led to conclude that whilst some fluids are capable of engendering both kinds of organisms, others tend only to produce one or other of them-whether the fluids are contained in closed flasks or in open vessels exposed to the incidence of atmospheric particles. I have more than once seen nothing but Torula appear in an infusion of turnip exposed to the air after it had been heated in a closed tube to a temperature of 293°F. for twenty minutes, and I have once seen the same thing occur in an unheated infusion of turnip exposed to the air, though on all other occasions such infusions have swarmed only with Bacteria and Vibriones. On the other hand, a boiled ammonic-tartrate solution exposed to the air, though protected from an excess of atmospheric particles (for the advent of a large number of these might in some cases incite putrefaction), is never found to contain Bacteria; the fluid continues clear, though a sediment gradually accumulates at the bottom of the flask, amongst which Torule and other fungus-germs are constantly to be found-more numerous though otherwise very similar to those which are to be met with in flasks closed during ebullition, or in others to which only filtered air is admitted. Although Torulæ only appear in such fluids, they continue all the time to be eminently inoculable by