Agricultural bacteriology : theoretical and practical / by John Percival.

  • Percival, John, 1937-2005.
Date:
1910
Catalogue details

Licence: In copyright

Credit: Agricultural bacteriology : theoretical and practical / by John Percival. Source: Wellcome Collection.

    55/434 (page 37)
    vessels containing the media to be sterilized have been placed within it, screw down the lid. The burners for heating the apparatus should now be lighted. Leave the stopcock open until steam begins to escape freely, then close it, and allow the pressure to rise until the gauge indicates i 5 lb., or a temperature of 1 1 5 to 1 2 5 °C. is reached. Lower the gas- burners, and allow the tempera- ture to remain at the figure just mentioned for half an hour ; then turn off the gas, and cool the autoclave to below 100 C. before opening the stopcock. Where the use of the auto- clave is prohibited on account of expense or for other reasons, liquids may be rendered sterile by the process of intermittent sterilization at a temperature of loo' C. or less. This is effected by heating to 100 ’ C. for twenty minutes on three or four succes- sive days. The first heating an active growing state, only spores present retaining their vitality. The latter are supposed to germinate in the cool intervals, the organisms arising from them being destroyed by the subsequent heating which they receive ; possibly the alternate heating and cooling on successive days may destroy ungerminated spores. For intermittent sterilization of media a steam sterilizer is used (Fig. 14). It consists of an iron or copper cylindrical vessel, covered on the outside with felt, asbestos or other