^{page 313 note *} This communication was originally made orally to the Royal Society on the 7th of April 1873. In preparing it for the press I have introduced various details which I was unable to enter upon at the time. I have also added facts ascertained at subsequent periods; but the dates of the observations being always mentioned, there will be no difficulty in distinguishing between those made before and after the delivery of the original address.

^{page 313 note †} In the present state of uncertainty regarding the true affinities of the yeast-plant, it seems justifiable to retain for it the old name Torula Cerevisiœ, a practice which has the advantage of enabling us to apply to similar budding cells the generic name Torula, and the adjective toruloid.

^{page 314 note *} This paper will also be found in the Quarterly Journal of Microscopical Science, vol. xi 1871.Google Scholar

^{page 315 note *} See Microscopical Journal, vol. xi. page 338.

^{page 315 note †} In an address delivered after the author had heen elected an honorary memher of the Society.

^{page 319 note *} There were, no doubt in reality eight: one of them being obscured by lying beneath the quadruple granule just formed out of one of the single ones.

^{page 321 note *} It may be urged that the particles of dust which give rise alike to the development of organisms and to fermentative changes in a fluid like urine are not necessarily organisms, but may possibly be little bits of so-called chemical ferments which occasion chemical alterations, that in their turn lead to the evolution of organisms by spontaneous generation. Such a view, plausible as it may appear, will be shewn in the sequel to be utterly destitute of scientific basis. Meanwhile we must be content with the sure step mentioned in the text, viz., the fact that neither fresh healthy urine nor its mucus contains any such evolutionary particles. I feel justified in stating this as a general truth regarding urine, since it has been found to hold not only in numerous other experiments with this liquid derived from the same source, but also when it was obtained by the same method from two other individuals.

^{page 323 note *} In preparing the liquid I deviated to some extent from Pasteur’s formula, -which is 100 parts distilled water, 10 parts pure sugar candy, 1 part tartrate of ammonia, and the ashes of 1 part of yeast. I employed lump-sugar instead of sugar candy, and reduced its proportion by one half, as it seemed to me likely to prove somewhat too strong to suit some organisms. Further, as I had not at hand a reference to enable me to ascertain how much of the mineral salts Pasteur employed, I used what seemed to me about a suitable amount for a fungus to consume, judging from the quantity that I got by incinerating a certain weight of yeast; and this, as I afterwards found, was a little more than Pasteur’s proportion. My solution, then, had the following composition:—

making rather more than half-a-pint. The liquid was introduced through a “ heated” funnel into a “ heated” Florence flask provided with a “ heated” glass cap, and was boiled and allowed to cool in the pure and covered vessel. A better method of procedure will be described in a later part of this communication.

^{page 324 note *} The efficacy of a strong watery solution of carbolic acid for the destruction of minute organisms was familiar to me from experience in antiseptic surgery; and it is also well illustrated by the method of obtaining uncontaminated unboiled urine described in the text. The fact is of great value in experiments on this subject, as it affords a simple and sure mode of purifying portions of apparatus which it would be inconvenient or impossible to subject to heat. And the extensive experience which this investigation has involved, enables me to state with confidence that wiping a piece of glass with a rag moistened with a solution of carbolic acid in twenty parts of water as efficiently destroys adhering organisms as heating to redness in a flame.

^{page 326 note *} It is indeed conceivable that a bacterium incapable of growing in fresh urine may have lain dormant in the liquid till it had become so altered under the influence of the torula as to be a suitable nidus for it. Meanwhile the fact of the morphological identity of this bacterium with buds from the filamentous fungus must be taken for what it is worth.

^{page 326 note †} I am not prepared to say whether the black colour which I have invariably found to be caused by the prolonged action of yeast upon Pasteur’s solution is due to the Torula Cerevisiœ or to other organisms accompanying it.

^{page 328 note *} The method by which this flask was prepared, and the mode of decanting into the experimental glasses, will be described in a later part of this paper.

^{page 329 note *} See De Bary, , Morphologie und Physiologie der Pilze, &c, Leipzig, 1866, p. 184Google Scholar.

^{page 335 note *} The Pasteur’s solution contained 1 per cent. of alcohol, for reasons with which I need not trouble the reader.

^{page 336 note *} Such glass gardens may be obtained of Messrs Sanderson, lapidaries, 92 Princes Street, Edinburgh.

^{page 337 note *} The actual order of proceeding is to introduce the boiled water into the air-chamber first, after which the same pipette, being clean, may be at once used for the liquid medium. I have found the most convenient form of pipette for these experiments to be a small syringe, having its nozzle connected, by means of a short piece of caoutchouc tubing, with a glass tube very narrow and thin, so that it is almost instantaneously heated nearly to redness by passing it through a flame, and cools with corresponding rapidity. The tube is bent near its middle at about a right angle; so that neither the syringe nor the hand is held over the experimental glass, while the yielding nature of the caoutchouc junction allows the end of the glass tube to be pressed, without risk of breaking, against any object, such as the side of a wineglass, from which an organism is being picked up.

^{page 342 note *} The actual time was much longer than I had intended, viz., two days. A subsequent experiment, in which one hour and twenty minutes was the period of immersion, was equally successful. Even after the two days of the present occasion, the carbolic acid did not seem to have affected the albumen, which was free from coagulation to the surface.

^{page 342 note †} This was a most troublesome procedure to carry out. I afterwards simplified the process very much, so as to dispense with both the spray and the filter, extracting the albumen with “ heated” pipette passed into a hole made in the carbolised shell with “ heated” forceps, a piece of carbolised cotton wool being wrapped round the pipette and egg to prevent entrance of dust, filtration of the mixture of albumen and water being effected by decanting through a boiled syphon, which had a piece of sponge tied over the end in the flask.