150 INFLUENCE OF PHYSICAL AGENTS. 



ments the spores of Bacillus anthracis and of Bacillus alvei failed to 

 grow after exposure to a temperature of 100 C. for four minutes, 

 and only a few colonies developed after two minutes' exposure to this 

 temperature. The thermal death-point of spores of the " wurtzel ba- 

 cillus " and of Bacillus butyricus (of Hueppe) was the same 100 C. 

 for four minutes. 



Schill and Fischer, in 1884, made a number of experiments to de- 

 termine the thermal death-point of Bacillus tuberculosis. They 

 found that five minutes' exposure to a temperature of 100 C. in 

 steam destroyed the vitality of the bacillus in sputum in five min- 

 utes. When the time was reduced to two minutes a negative result 

 from inoculation was obtained in two guinea-pigs, but one inoculated 

 at the same time became tuberculous. My own experiments and 

 those of Yersin, made since, lead me to think that there may have 

 been some cause of error in this experiment of Schill and Fischer, 

 and that the thermal death-point of the spores of Bacillus tuber- 

 culosis is considerably below the boiling point of water. I inoculated 

 guinea-pigs with tuberculous sputum subjected for ten minutes to 

 the following temperatures : 50, 60, 70, 80, 90 C. The animal 

 inoculated with material exposed to 50 died from tuberculosis at the 

 end of seven weeks. None of the others developed tuberculosis. 



Yersin exposed an old culture in glycerin bouillon, in which many 

 of the bacilli contained spores "tres nettes" to the following tem- 

 peratures : 55, 60, 65, 70, 75, 80, 85, 90, 100 C. " At the end of 

 ten days the bacilli heated to 55 gave a culture in glycerin bouillon ; 

 those exposed to 60 grew after twenty-two days ; none of the 

 bacilli heated above 70 gave any development. This experiment, 

 repeated a great number of times, has always given us the same re- 

 sult." Voelsh, who has studied the same question, reports as the 

 result of his experiments that the tubercle bacillus in sputum was 

 not destroyed by heating to 100 C. Further experiments will be re- 

 quired to reconcile these contradictory results. 



While the spores of the pathogenic bacteria mentioned are de- 

 stroyed by the boiling point of water within a few minutes, certain 

 non-pathogenic species resist this temperature for hours. Thus 

 Globig obtained a bacillus from the soil the spores of which required 

 five and one-half to six hours' exposure to streaming steam for their 

 destruction. These spores survived exposure for three-quarters of an 

 hour in steam under pressure at from 109 to 113 C. They were de- 

 stroyed, however, by exposure for twenty-five minutes in steam at 

 113 to 116, and in two minutes at 127. 



In the practical application of steam for disinfecting purposes it 

 must be remembered that, while steam under pressure is more effec- 

 tive than streaming steam, it is scarcely necessary to give it the pre- 



