TAILIEUCHUNG - YEAST

I HAVE selected to-night the particular subject of Yeast for two reasons—or, rather, I should say for three. In the first place, because it is one of the simplest and the most familiar objects with which we are acquainted. In the second place, because the facts and phenomena which I have to describe are so simple that it is possible to put them before you without the help of any of those pictures or diagrams which are needed when matters are more complicated, and which, if I had to refer to them here, would involve the necessity of my. | YEAST By Thomas H. Huxley I HAVE selected to-night the particular subject of Yeast for two reasons or rather I should say for three. In the first place because it is one of the simplest and the most familiar objects with which we are acquainted. In the second place because the facts and phenomena which I have to describe are so simple that it is possible to put them before you without the help of any of those pictures or diagrams which are needed when matters are more complicated and which if I had to refer to them here would involve the necessity of my turning away from you now and then and thereby increasing very largely my difficulty already sufficiently great in making myself heard. And thirdly I have chosen this subject because I know of no familiar substance forming part of our every-day knowledge and experience the examination of which with a little care tends to open up such very considerable issues as does this substance yeast. In the first place I should like to call your attention to a fact with which the whole of you are to begin with perfectly acquainted I mean the fact that any liquid containing sugar any liquid which is formed by pressing out the succulent parts of the fruits of plants or a mixture of honey and water if left to itself for a short time begins to undergo a peculiar change. No matter how clear it might be at starting yet after a few hours or at most a few days if the temperature is high this liquid begins to be turbid and by-and-by bubbles make their appearance in it and a sort of dirty-looking yellowish foam or scum collects at the surface while at the same time by degrees a similar kind of matter which we call the lees sinks to the bottom. The quantity of this dirty-looking stuff that we call the scum and the lees goes on increasing until it reaches a certain amount and then it stops and by the time it stops you find the liquid in which this matter has been formed has become altered in its quality. To begin with it was a mere sweetish

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