156 ANTISEPTIC AND GERMICIDAL POWER 



of the addition of these organic substances is in every case to 

 considerably lower the coefficient obtained with what may be 

 styled the naked germs, but the coefficient of some disinfectants 

 (for example, potassium permanganate) is lowered to a much 

 greater degree than others. 



Organic matter method of Chick and Martin. 



The method adopted by Chick and Martin, in which dried 

 faeces is used, is a useful one. It is carried out as follows : 



The faeces used is dried, first in a water-bath then at 105 C, 

 ground to a fine powder, and passed through a fine sieve with a 

 mesh of 130 to the inch. Quantities of 0*15 gramme are weighed 

 out and placed in test-tubes, to which also are added 2' 5 c.c. 

 of distilled water. The tubes are sterilized in the autoclave, 

 covered with indiarubber caps, and stored in covered jars. 



At the time of the experiment different amounts of a suitable 

 dilution of the disinfectant are added to each tube, together with 

 enough distilled water to make the total volume 5 c.c. The 

 tubes then contain different concentrations of the disinfectant in 

 the presence of 3 per cent, faeces. 



The tubes are then placed in a water-bath at 20 C. When 

 the tubes have taken the temperature of the bath, they are one 

 after another inoculated with five drops of twenty-four hours' 

 culture of B. typhosus from a standard pipette, the time being 

 registered by a chronograph. Exactly one minute is allowed 

 to pass between each inoculation. When thirty minutes have 

 elapsed since the first tube was inoculated, samples in duplicate 

 are taken from it with a platinum loop (of standard size), and 

 sown in 10 c.c. litmus glucose broth. One minute later the 

 second tube is sampled, and so on. The test cultures are incu- 

 bated at 37 C., and always kept four days under observation. 

 For the first testing a wide series of dilutions must be employed. 

 The second series may be narrowed down, and at the last trial, 

 which may be the second or third series, a series of tubes 

 containing various strengths of pure phenol are simultaneously 

 treated. 



