. A text-book of comparative physiology for students and practitioners of comparative (veterinary) medicine . e student of physiologyand medicine. To state, first, the main facts as ascertained byobservation and experiment : Morphological.—The particles of which yeast is composedare cells of a circular or oval form, of an average diameter ofabout s-gVo of an inch. Each individual torula cell consists of a transparent homo-geneous covering (cellulose) and granular semifluid contents(protoplasm). Within the latter there may be a space (vacu-ole) filled with more fluid contents. The various cells
. A text-book of comparative physiology for students and practitioners of comparative (veterinary) medicine . e student of physiologyand medicine. To state, first, the main facts as ascertained byobservation and experiment : Morphological.—The particles of which yeast is composedare cells of a circular or oval form, of an average diameter ofabout s-gVo of an inch. Each individual torula cell consists of a transparent homo-geneous covering (cellulose) and granular semifluid contents(protoplasm). Within the latter there may be a space (vacu-ole) filled with more fluid contents. The various cells produced by budding may remain unitedlike strings of beads. Collections of masses composed of fouror more subdivisions (ascospores), which finally separate by rup-ture of the original cell wall, having thus become themselves in-dependent cells, maybe seen more rarely (endogenous division). The yeast-cell is now believed to possess a nucleus. Chemical.—When yeast is burned and the ashes analyzed,they are found to consist chiefly of salts of potassium, calcium,and magnesium. 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 dryingyeast 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 mixtureto become frothy; andthe fluid will acquirean alcoholic charac-ter {fermentation). If the mixture beraised to the boiling-point, the process de-scribed at once ceases. It may be furthernoticed that in thefermenting saccha-rine solution there isa gradual increase ofturbidity. All of thesechanges go on per-fectly well in the to-tal absence of sun-light. Yeast - cells arefound to grow andreproduce abundant-ly iu an artificial foodsolution consisting ofa dilute solution of Fig. 4.—Further development of the forms represented certain Salts, togetherin Fig.
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Keywords: ., bookcentury1800, bookdecade1890, bookpublishernewyo, bookyear1890
