. Civic biology; textbook of problems, local and national, that can be solved only by civic coöperation. Biology. 192 CIVIC BIOLOGY compressed yeast contains approximately 10,000,000,000 of them. In order, once for all, to gain a notion of the minuteness of microorganisms, perform the following simple experiment: Sharpen the point of a teasing-needle to a tine knife bhide ; lake a bit of moist compressed yeast, the size of a large pinhead, on a piece of clean, polished glass (a microscope slide) and cut the lump in halves. Throw away one half and repeat the operation and continue as long as yo
. Civic biology; textbook of problems, local and national, that can be solved only by civic coöperation. Biology. 192 CIVIC BIOLOGY compressed yeast contains approximately 10,000,000,000 of them. In order, once for all, to gain a notion of the minuteness of microorganisms, perform the following simple experiment: Sharpen the point of a teasing-needle to a tine knife bhide ; lake a bit of moist compressed yeast, the size of a large pinhead, on a piece of clean, polished glass (a microscope slide) and cut the lump in halves. Throw away one half and repeat the operation and continue as long as you can see to divide the particle. At the last division carefully plant one half in a vial half full of filtered, boiled molasses and water (a table- spoonful of molasses in half a pint of potato water makes a good cul- ture fluid), to watch it grow from day to day. Then, with the point of a clean needle, on a perfectly clean part of the glass, cover the other half with a minute droplet of water. Cover with a per- fectly clean cover glass and try to count the tor- ulae (yeast plants) in the speck that you can just see with the naked Fig. 93. Yeast plants, highly magnified, show- ing successive stages of growth by budding After Conu In color most of the common yeasts, when seen in mass, are whit- ish or slightly yellowish gray, the color of a fresh yeast cake, but a few species are pink, red, or black. Distribution. Y^easts are everywhere; so the question is not, Where shall we go to find them, but. Where go to escape them ? We eat them by billions, baked, in our daily bread ; we drink them by millions, alive, in our eider, beer, or Avine : we breathe them in, alive, with e^ery breath, and drink them, alive or dead, according as the water is raw or ])oiled, with every drink of water we take; they are all over us all the time, in our hair, on our skins, in all our clothes, and we cannot possibly beat them out, brush them off, or e*^^en wash them away — the harmless, usefu
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