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.

    11/16 (page 3)
    during the few moments it is exposed to the air, it grows exactly upon the spot upon which it fell, and can be easily recognized as a stranger. To maintain the colonies isolated from one another during their growth, and free from contamination, it is only necessary to thin out the micro-organisms sufficiently, and to limit the exposure of the plates to the air to as short a time as possible, both during their preparation and during their subsequent examination. The result will depend upon the way in which the thinning or fractional cultivation has been carried out, and the colonies will be found to develope in the course of a day or two, the time varying with the rapidity of growth of the micro-organism and the tem- perature of the room. If we have prepared three plates, we shall commonly find that the lower plate will contain a countless number of colonies which, if the micro-organism liquefies gelatin, speedily commingle and produce in a very short time a complete liquefaction of the whole of the nutrient medium. In the middle plate or “ the first thinning,” the colonies will also be very numerous; while in the uppermost plate, “ the second thinning,” the colonies are com- pletely isolated from one another, with an appreciable surface of gelatin intervening. The microscopical appearances of the colonies can perhaps best be observed by placing the plate upon a slab of blackened plate glass, or upon a porcelain slab if the colonies are coloured. The microscopical appearances are examined by placing a selected plate upon the stage of the Microscope, and it is better to have a larger stage than usual for this purpose. The smallest diaphragm is employed, and the appearances studied principally with a low power. The morphological characteristics of the micro-organisms of which the colony is formed can then be examined in the following way. A platinum needle bent at the extremity into a miniature hook is held like a pen, and the hand steadied bv resting the little finger on the stage of the Microscope. The extremity of the needle is steadily directed between the lens and the gelatin with out touching the latter, until on looking through the Microscope it can be seen in the field above, or by the side of the colony under examination. The needle is then dipped into the colony, steadily raised, and withdrawn. Without removing the eye from the Microscope, this small operation may be seen to be successful, by the colony being disorganized or completely removed from the gelatin. It is, however, not easy to be successful at first, but with practice this can be accomplished with rapidity and precision. A cover-glass preparation is then made in the usual manner, by rubbing the extremity of the platinum needle in a droplet of 13 2 [27]