The micro-organisms of fermentation practically considered / by Alfred Jörgensen.

  • Jörgensen, Alfred, 1848-1925.
Date:
1889
Catalogue details

Licence: Public Domain Mark

Credit: The micro-organisms of fermentation practically considered / by Alfred Jörgensen. Source: Wellcome Collection.

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    to determine the size of tliis voluine; it is then only necessary to ahvays work witli tlie same voluine. It is always necessary tliat the sample taken be a fair average one. In most cases tliis must be diluted and tborougbly agitated for a long time, in Order to obtain an equal distribution of tbe cells ; tbe specific gravity of tbe liquid must also be such tbat it will allow tbe cells to remain suspended in it for a sbort time. A small drop is tben witbdrawn witb a capillary tube, transferred to tbe counting apparatus, and covered witb a cover-glass. Tbe apparatus is now allowed to remain at rest for some time ; tbe cells are tben able to settle at tbe bottom of tbe defined space, and on tbis account tbe specific gravity of the liquid must not be greater tban wdll allow tbis to take place in a convenient time. Botb tbese requirements are generally satisfied by tbe wort used for industrial operations. If it is found tbat tbe determinate volume still contains too many cells to be counted witb certainty, tbe liquid must be furtber diluted. Tbis may also be advisable for other reasons : partly to prevent tbe formation of frotb, wbicb generally forms abmidantly from tbe violent agita- tion, and partly to isolate tbe single cells wbicb, in wort, are frequently collected togetber in colonies or large masses, and are not always separated by shaking, and, finally, in Order to bring about tbe discontinuation of tbe fermentation and tbe multiplication of tbe yeast-cells after tbe beginning of tbe experiment. Hansen found tbat dilute sulpburic acid (1 : 10) completely answered tbese requirements ; bydrocbloric acid, ammonia, and caustic soda may also be used, but tbey are not so good. If a very great dilution is required, distilled water can be added, after tbe addition of 1 to 2 volumes of dilute sulpburic acid. Wben tbe different volumes of liquid are mixed witb accuracy, and care taken tbat tbe cells are tborougbly dis- tributed by violent and prolonged shaking, tbe determination can be made witb great exactness. Two similar dilutions must always be made, and samples from eacb taken for