154 ANTISEPTIC AND GERMICIDAL POWER 



at the 2j minutes' line and at the 30 minutes' line, and a mean 

 of -the resulting figures was taken as the carbolic acid coefficient." 



Method of Chick and Martin. 



Chick and Martin 1 have also modified the method using a 

 standard time (30 minutes). They describe their procedure as 

 follows : 



"Everything used in the experiment, tubes, pipettes, etc., 

 being previously sterilized, a series of tubes containing 5 c.c. of 

 the disinfectant in different concentrations are 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 24 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 30 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. glucose broth containing litmus. One 

 minute later the second tube is sampled and so on. These test 

 cultures are incubated at 37 C. and always kept four days 

 under observation." 



Preliminary observations are necessary to narrow down the 

 dilutions likely to be lethal. At the last trial a series of tubes, 

 containing various strengths of pure phenol are simultaneously 

 tested. 



Modifying influences. 



The Rideal-Walker procedure and its modifications furnish 

 valuable information, but the results obtained cannot be applied 

 without extensive modification to the practical use of disinfec- 

 tants. The utility of any disinfectant depends upon a number of 

 different factors. The most important of these is how far it is 

 uninfluenced by the presence of organic matter. The efficiency 

 of some disinfectants is greatly altered by the presence of 

 organic matter, while for others only a comparatively slight 

 diminution of power is so caused. 



1 Journal of Hygiene , 1908, vol. VIII, p. 654. 



