On the cultivation of bacteria / by Edgar M. Crookshank.

  • Edgar Crookshank
Date:
[1886]
Catalogue details

Licence: Public Domain Mark

Credit: On the cultivation of bacteria / by Edgar M. Crookshank. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    the very first: if then we require to isolate one species from the rest, the expenditure of much time is involved. For example, to attain this object it was proposed, in the method of fractional dilution, to add sterilized nutrient fluid until there was an average of less than one germ to each drop of the fluid. If, then, fresh portions of sterilized nutrient fluid be inoculated with a single drop from the diluted mixture, some portions would in all probability receive no microbes, others would receive one or two, and others, again, one or more microbes of the same species. Then the growth of these microbes would give a pure cultivation of a particular species. It is obvious how com- plicated this process is, and how much the result would depend upon chance. If, on the other hand, the mixture was left as a mixture, then the door was open to all sorts of conclusions. Some bacteria being unable to develope in the presence of others, or a change of tem- perature, or a change effected by the micro-organisms in the nourishing soil, allowing one form to predominate over another, the idea could arise that the various kinds of bacteria were but developmental forms of one and the same micro-organism. Further, very probably contamination of such cultivations led to the belief in the transformation of a harmless into a pathogenic bacterium. In the case of solid cultivating media, on the other hand, the possible contamination of the nourishing ground by the gravita- tion of germs from the air is guarded against, not by elaborate apparatus or ingenious devices, but by the simple fact that test- tubes, flasks and other vessels can be inverted, and are inoculated from below. The great secret of success in Koch’s methods of cultivation consists in that we are able, from a mixture of micro-organisms, to isolate the individual species and establish a pure cultivation of each distinct form. By the same method, which is remarkable for its simplicity, if by any possibility contamination has occurred, we can separate the adventitious microbe and regain a pure cultivation. This is accomplished in the following manner. A test-tuhe containing sterilized nutrient gelatin is warmed, and the lique- fied jelly is then inoculated with a platinum needle from the mixture of bacteria, in such a way that the individual micro- organisms are distributed throughout the liquid medium. The liquid is then poured out upon a plate of glass, and allowed to solidify. The individual bacteria, instead of moving about freely as in a liquid medium, are fixed in one spot, where they develope individuals ot their own species. In this way colonies are formed, each possessing its own characteristic biological and morphological appearances; if an adventitious germ fall upon the cultivation [26]