EFFECT OF TEMPERATURE UPOX THE GROWTH OF BACTERIA 45 



one hour, practically all spores are killed. Moist heat at a temperature 

 of 100 C., either boiling water or free-flowing steam, destroys the 

 spores of known pathogenic bacteria within fifteen minutes; certain 

 non-pathogenic species, however, resist this temperature for hours. The 

 spores of a bacillus from the soil required five and a half to six hours' 

 exposure to streaming steam for their destruction. They were destroyed, 

 however, by exposure for twenty-five minutes in steam at 113 to 116 C. 

 and in two minutes at 127 C. 



The resistance of spores to moist heat is tested by suspending threads, 

 upon which the spores have been dried, in boiling water or steam. The 

 threads are removed from minute to minute and laid upon agar or in 

 broth, which is then placed at a suitable temperature. 



Practical Use of Heat Disinfection. In the practical application of 

 steam for disinfecting purposes it must be remembered that while moist 

 steam under pressure is more effective than streaming steam it is scarcely 

 necessary to give it the preference, in view of the fact that most known 

 pathogenic bacteria produce no spores and the spores of the few that do 

 develop them are quickly destroyed by the temperature of boiling water, 

 and also that "superheated" steam is less effective than moist steam. 

 When confined steam in pipes is "superheated" after its generation it has 

 about the same germicidal power as hot, dry air at the same temperature. 

 Esmarch found that anthrax spores were killed in streaming steam in 

 four minutes, but were not killed in the same time by superheated steam 

 at a temperature of 114 C. It should also be remembered that dry heat 

 has but little penetrating powder, and that even steam requires time to 

 pass through heavy goods. Koch and Wolff hugel found that registering 

 thermometers placed in the interior of folded blankets and packages 

 of various kinds did not show a temperature capable of killing bacteria 

 after three hours' exposure in a dry hot-air oven at 133 C. and over. 

 We have often put a piece of ice in the middle of several mattresses and 

 recovered it after exposing the goods to an atmosphere of live steam for 

 ten minutes. 



FRACTIONAL STERILIZATION. Certain nutrient media, such as blood- 

 serum and the transudates of the body cavities, as well as certain fluid 

 foodstuffs, need at times to be sterilized, and yet cannot be subjected 

 to temperatures high enough to kill spores without suffering injury. 

 The property of spores, when placed under suitable conditions, to germi- 

 nate into the non-spore bearing form, is here taken advantage of by 

 heating the fluids up to 55 to 70 C. for one hour on each of six con- 

 secutive days, and keeping the fluid at about 20 C. during the intervals. 

 By this means we kill, upon each exposure, all bacteria in the vegetative 

 form, and allow, during the intervals, for the development of any still 

 remaining in the spore stage, or which have reproduced spores, to 

 change again into the vegetative form. Experience has shown that, 

 with but few exceptions, an exposure for six consecutive days will com- 

 pletely sterilize the fluids so exposed. 



With the usual culture media a temperature of 100 C. for twenty 

 minutes does little or no harm while one of 115 C. is deleterious. With 



