THE DESTRUCTION OF BACTERIA 65 



Radium rays have a distinct inhibitory and even bactericidal 

 power when applied at distances of a few centimeters for several 

 hours. 1 



Electricity. If we exclude the indirect actions of heat and electro- 

 lysis, it can hardly be said that the direct bactericidal action of electric 

 currents has been satisfactorily demonstrated. Such action, however, 

 has been claimed by d'Arsonville and Charrin, 2 and by Spilker and 

 Gottstein. 3 



Heat. The most widely applicable and efficient physical agent for 

 sterilization is heat. 



The dependence of bacteria for growth and vitality upon the main- 

 tenance of a proper temperature in their environment, and the ranges 

 of variation within which bacteria may thrive, have been discussed in a 

 preceding section, in which a table of so-called " thermal death points " 

 has been given. In the method of expressing these values it was seen 

 that two elements entered into the destruction of bacteria by heat, 

 namely, that of the degree of temperature which is applied, and that of 

 the time of application. 



The prolonged application of moderately high temperatures, in other 

 words, may in certain instances, accomplish the same result as the brief 

 use of extremely high ones. In general, the death of bacteria following 

 prolonged exposure to temperatures but slightly exceeding the optimum 

 is due to the inability of the anabolic processes to keep pace with the 

 accelerated katabolic processes, gradual attenuation resulting in death. 

 At somewhat higher temperatures death results from coagulation of 

 the bacterial protoplasm, and at still higher degrees of heat, applied in 

 the dry form, direct burning of the bacteria may be the cause of their 

 destruction. 



Heat may be applied in the form of dry heat or as moist heat, these 

 methods being of great practical value, but differently applicable ac- 

 cording to the nature of the materials to be sterilized. The two methods, 

 moreover, show a marked difference in efficiency, temperature for tem- 

 perature. For the recognition of this fact we are largely indebted to the 

 early researches of Koch and Wolffhiigel, 4 and of Koch, Gaffky, and 

 Loeffler. 5 



1 Personal observations. 



2 D'Arsonville and Charrin, Compt. rend, de la soc. de biol. 

 s Spilker and Gottstein, Cent. f. Bakt., I, 9, 1891. 



4 Koch und Wolffhiigel, Mitt. a. d. kais. Gesundheitsamt, 1, 1882. 



5 Koch, Gaffky and Loeffler, ibid. 



