INFLUENCE OF PHYSICAL AGENTS. 



151 



an air chamber. A little material from a pure culture of the test organ- 

 ism is drawn into each of these capillary tubes by immersing the open 

 extremity in the culture, after having- gently heated the expanded end. The 

 end of the tube is then hermetically sealed by heat. These tubes are im- 

 mersed in a water bath maintained at the desired temperature for the stan- 

 dard time. The bath is kept at a uniform temperature by personal supervi- 

 sion. At the bottom of the vessel is a thick glass plate which prevents the 

 thermometer bulb and capillary tubes, which rest upon it, from being ex- 

 posed to heat transmitted directly from the bottom of the vessel. To further 

 guard against this I am in the habit of applying the flame to the sides of the 

 vessel, and a uniform temperature throughout the bath is maintained by 

 frequent stirring with a glass rod. It is impossible to avoid slight variations, 

 but by keeping my eye upon the thermometer throughout the experiment 

 I have kept these within very narrow limits. ... No attempt has been made 

 to fix the thermal death-point within narrower limits than 2 C., and in the 

 table the lowest temperature is given which has been found, in the experi- 

 ments made, to destroy all of the microorganisms in the material subjected 

 to the test. No doubt more extended experiments would result, in some in- 

 stances, in a reduction of the temperature given as the thermal death-point 

 for a degree or more. But the results as stated are sufficiently accurate for 

 all practical purposes." ' 



The results obtained in these experiments, for non-sporebearing 

 bacteria, are given in the following table. The time of exposure 

 was ten minutes, except for the cholera spirillum and the cheese spi- 

 rillum of Deneke. 



THERMAL DEATH-POINT OF BACTERIA.. 



The following determinations of the thermal death-point of path- 



1 Quoted from the Report of the Committee on Disinfectants of the American Pub- 

 lic Health Association, pages 136 and 152. 



