The effect of physical agents on bacterial life / Sir James Crichton-Browne, M.D. LL.D. F.R.S., Treasurer and Vice-President, in the chair. Allan Macfadyen, M.D., Bsc., Director of the Jenner Institute of Preventive Medicine.

  • James Crichton-Browne
Date:
[1900?]
Catalogue details

Licence: In copyright

Credit: The effect of physical agents on bacterial life / Sir James Crichton-Browne, M.D. LL.D. F.R.S., Treasurer and Vice-President, in the chair. Allan Macfadyen, M.D., Bsc., Director of the Jenner Institute of Preventive Medicine. Source: Wellcome Collection.

    6/12 (page 6)
    Ozone is a powerful disinfectant, and its introduction into pollute water has a most marked purifying effect. The positive effects c the electric current may therefore be traced to the action of th chemical products and of heat. I am not aware that any direct actio of the X-rays on bacteria has up to the present been definitel proved. Mechanical agitation, if slight may favour, and if excessive ma hinder bacterial development. Violent shaking or concussion ma not necessarily prove fatal so long as no mechanical lesion of th bacteria is brought about. If, however, substances likely to produc triturating effects are introduced, a disintegration and death of th cells follows. Thus Rowland, by a very rapid shaking of tubercl bacilli in a steel tube with quartz sand and hard steel balls, produce' their complete disintegration in ten minutes. Bacteria appear to be very resistant to the action of pressun At 300-450 atmospheres putrefaction still takes place, and at 601 atmospheres the virulence of the anthrax bacillus remained unim paired. Of the physical agents that affect bacterial life, tempera ture is the most important. Temperature profoundly influence the activity of bacteria. It may favour or hinder their growth, o it may put an end to their life. If we regard temperature ii the first instance as a favouring agent, very striking difference! are to be noted. The bacteria show a most remarkable range o temperature under which their growth is possible, extending fron zero to 70° C. If we begin at the bottom of the scale we fim organisms in water and in soil that are capable of growth an< development at zero. Amongst these are certain species of phosphor escent bacteria which continue to emit light even at this low tempera ture. At the Jenner Institute we have met with organisms growing and developing at 34-40° F. The vast majority of interest to us fim however the best conditions for their growth from 15° up to 37° C Each species has a minimum, an optimum and a maximum tempera ture at which it will develop. It is important in studying any givei species that the optimum temperature for their development b' ascertained, and that this temperature be maintained. In thi respect we can distinguish three broad groups. The first grou] includes those for which the optimum temperature is from 15-20° C The second group includes the parasitic forms, viz. those which grov in the living body and for which the optimum temperature is a blood heat, viz. 37° C. We have a third group for which th optimum temperature lies as high as 50-55° C. On this accoun this latter group has been termed thermophilic on account of iti growth at such abnormally high temperatures—temperatures whicl are fatal to other forms of life. They have been the subject o: personal investigation in conjunction with Dr. Blaxall. We founc that there existed in nature an extensive group of such organisms t< which the term thermophilic bacteria was applicable. Their growtl and development occurred best at temperatures at which ordinary