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

  • Alfred Jørgensen
Date:
1889
Catalogue details

Licence: Public Domain Mark

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

    24/198 page 2
    of bread, tlie cultivation was carefully covered with a glass sliade, and all possible precautions were observed in Order to protect tlie growth from external contamination. After some days a growtb of mould appeared, as is always the case wlien moist bread is placed under these conditions ; and tlie conclusion was tberefore drawn tliat beer-yeast was the origin of the mould forms, and that, consequently, yeast- and mould-fvmgi were different phases of growth of the same species. A number of years elapsed before what now appear to be the most self-evident requirements of this dass of investiga- tions were put in practice, before it was possible to be certain from 'which point to start in order to arrive at a definite condusion. These requirements were gradually practised with greater care, and at last, as we shall see later, a point w'as reached which satisfies in the highest degree both the demands of our subject and also those of the closely related branches of Science. A microscope capable of giving a magnification of 1,000 diameters is, as a rule, necessary for the investigation of micro-organisms. For the yeast- and mould-fungi the only preparation generally required consists in placing a drop of the liquid contaiuing the organism on a glass shde, and spreading it out in a thin layer by means of a cover-glass. When cultivated, qn sohd substances, a very small portion of the growth is first mixed with a drop of water. The preliminary examination of bacteria also must always be carried out in the above manner. In the latest investigations with bacteria, and especially with the pathogenic forms, a number of different methods of drying and staining are employed, partly in order to facihtate the examination, and partly in order to bring out characteristics which would otherwise be observed only with diflficulty or not at all. An objection to these methods, urged with undoubted correctness, is that the violent treatment often alters certain proportions of the bacteria ; for instance, the proportion of length and thickness. On the other hand, it must be admitted, espe- cially with regard to certain pathological forms—the tubercle-
    digitised image 1
    digitised image 2
    digitised image 3