. A text-book of comparative physiology for students and practitioners of comparative (veterinary) medicine. Physiology, Comparative. 10 COMPARATIVE The elements of which, yeast is composed are C, H, O, N, S, P, K, Mg, and Ca; but chiefly the first four. Physiological.—If a little of the powder obtained by drying yeast at a temperature below blood-heat be added to a solution of sugar, and the lat- ter be kept warm, bubbles of carbon di- oxide will be evolved, causing the mixture to become frothy; and the fluid will acquire an alcoholic charac- ter (fermentation). If the mixture be
. A text-book of comparative physiology for students and practitioners of comparative (veterinary) medicine. Physiology, Comparative. 10 COMPARATIVE The elements of which, yeast is composed are C, H, O, N, S, P, K, Mg, and Ca; but chiefly the first four. Physiological.—If a little of the powder obtained by drying yeast at a temperature below blood-heat be added to a solution of sugar, and the lat- ter be kept warm, bubbles of carbon di- oxide will be evolved, causing the mixture to become frothy; and the fluid will acquire an alcoholic charac- ter (fermentation). If the mixture be raised to the boiling- point, the process de- scribed at once ceases. It may be further noticed that in the fermenting, saccha- rine solution there is a gradual increase of turbidity. All of these changes go on per- fectly well in the to- tal absence of sun- light. Yeast - cells are found to grow and reproduce abundant- ly in an artificial food solution consisting of a dilute solution of Fie. 4.—Farther development of the forms represented certain salts tOffether in Fig. 3. ' & . With sugar. Conclusions.—What are the conclusions which may be legiti- mately drawn from the above facts ? That the essential part of yeast consists of cells of about the size of mammalian blood-corpuscles, but with a limiting wall of a substance different from the inclosed contents, which latter is composed chiefly of that substance common to all living things—protoplasm; that like other cells they reproduce their FiQ. 2.—Varions stages in the development of brewer's yeast, seen, with the exception of the first in the series, with an ordinary high power (Zeiss, B. 4) of the microscope. The first is greatly magnified {Gundlach's A Immersion lens). The secondseries of four represents stages in the division of a single cell ; and the third series a branching colony. Everywhere the light areas indicate Please note that these images are extracted from scanned page images that may
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