ComiJarative Poiver of some Disinfectants. 95 



Tartrate of ammonia . . . 



2 



Sulphate of magnesia... ... 1 



Acid phosphate of potash ... ... ... 1 



Chloride of calcium ... ... ... ... tV 



Distilled water 200 



When this solution is boiled and preserved from any con- 

 tamination it remains clear for an indefinite time ; but if the 

 smallest portion of any substance containing the septic 

 organisms, called by botanists the haderium termio, is added, 

 it gradually becomes milky, the rapidity with which this 

 occurs varying with the temperature at which the fluid is 

 kept. The mode of procedure which I adopted was as 

 follows : — I obtained a supply of the bacteria by adding a 

 few crushed peas to warm water and leaving the mixture 

 till it emitted a putrid smell, when it was found on micro- 

 scopic examination to be swarming with these and other 

 organisms. Then, to obtain them free from admixtures, 

 I inoculated a portion of Cohn's solution with a minute 

 drop of this putrid fluid, with the result that in less than 

 two days the previously limpid solution had become quite 

 opalescent. The bottle in which it was contained was 

 shaken up, so as to obtain a uniform mixture, and a piece of 

 filter-paper soaked with this, and then carefully dried in the 

 sun for several hours. This bacterialised paper was pre- 

 sers^ed between the leaves of a book, and small portions of 

 it used as required. To guard against fallacies I used the 

 following precautions : — A number of small phials were taken, 

 containing each about a fiuid dram of Cohn's solution, and 

 after being carefully plugged with baked cotton wadding, 

 they were kept immersed in boiling water for a few minutes, 

 so as to ensure the destruction of any bacteria which might 

 by chance have obtained admission. After cooling, a portion 

 of the bacterialised paper, which had been subjected to some 

 disinfecting process, was put into one of them, the plug being 

 removed for as short a time as possible. For the purpose of 

 saving time a number of phials were thus charged and put 

 aside in some protected place at the ordinary house temper- 

 ature. As a check I placed beside them one phial to which 

 nothing was added, and another into which a piece of the 

 bacterialised paper, pure and simple, of the same size as the 

 others, was put. If the phial containing only boiled Cohn's 

 solution remained clear, this was a proof that there had been 

 no accidental contamination, while if the one to which 



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