CHAPTER XI 



THE SOLUTIONS EMPLOYED ARE NOT PRONE TO BE 

 CONTAMINATED BY AIR-BORNE PARTICLES 



Six tubes that had been heated to 130 C., in 

 which no organisms had been found (four con- 

 taining the colourless and two the yellow solu- 

 tion) , were left in my study for six to eight weeks, 

 standing upright, the opening in each tube being 

 about one third of an inch in diameter, so that 

 dust particles could readily fall into the solutions. 



The fluids, however, remained perfectly clear; 

 and on microscopical examination of the deposit 

 no organisms were still to be found after the 

 periods mentioned. 



This induced me to make other experiments 

 bearing upon this question. I took four two- 

 ounce sterilised flasks, and charged each of them 

 with one ounce of the colourless fluid, which was 

 then boiled in each of them for ten minutes. Two 

 of the flasks had a nicked rubber stopper, which, 



after the cessation of the ebullition, was pressed 



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