THE DESTRUCTION OF BACTERIA 79 



others to be without appreciable germicidal power. Rieder, 18 011 

 the other hand, has reported definite inhibition of bacterial growth 

 after exposures of half an hour to X-rays. 



Radium rays have a distinct inhibitory and even bactericidal 

 power when applied at distances of a few centimeters for several 

 hours. 19 



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

 trolysis, 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, 20 and by 

 Spilker and Gottstein. 21 



Heat. The most widely applicable and efficient physical agent 

 for sterilization is heat. 



The dependence of bacteria for growth and vitality upon the 

 maintenance 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 express- 

 ing these values it was seen that two elements entered into the 

 destruction of bacteria by heat, namely, that of the degree of tem- 

 perature 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 tem- 

 peratures 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 ap- 

 plicable according to the nature of the materials to be sterilized. 

 The two methods, moreover, show a marked difference in efficiency, 



18 Eicder, Munch, med. Woeh., 1898. 

 1U Personal observations. 



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



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



