146 STERILIZATION AND DISINFECTION 
in the method by working with anthrax spores. The Rideal-Walker 
method does not consider the presence of organic matter. 
Chick and Martin’s Modification of the Rideal-Walker Method. 
These authors have pointed out that an arbitrary time must be selected 
during which the disinfectant shall be allowed to act. The Ridcal- 
Walker method is modified with this in view. The proccdure is as 
follows: 
WirHout OrGANic MATTER 
Everything used in the experiment, tubes, pipettes, etc., being 
previously sterilized, a series of tubes containing 5 c.c. of 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 a twenty-four hour culture of B. 
typhosus from a standard pipette, the time being registered by a 
chronograph. Exactly one minute is allowed to pass between cach 
inoculation. When thirty minutes have elapsed since the first tube 
was inoculated, samples in duplicate are taken from it with a platinum 
loop, and sown in 10 c.c. glucose broth containing litmus. One min- 
ute later the second tube is sampled and so on. These test cultures 
are incubated at 37° C. and always kept four days under observation. 
Supposing the value of the disinfectant to be tested is totally 
unknown, the first series of observations must be scattered over a 
wide range, e.g., concentrations from 1 in 10 to 1 in 10,000. Having 
ascertained that the concentration necessary to kill in thirty minutes 
is between, say, 10 in 1000 and 1 in 1000 the second series is arranged 
to narrow it down to between, say, 4 and 5 per 1000, and a third series 
may determine the necessary concentration as between 4.2 and 4.5 
per 1000. At this last trial a series of tubes, containing various 
strengths of pure phenol, are simultaneously tested. 
Wits OrGcanic MatrrerR 
In order to determine the effect of the presence of organic matter, 
Chick and Martin use dried, pulverized feces as follows: 
The feces used were dried first in a water bath and subsequently 
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 germs were weighed 
out and placed in test tubes. To each test tube 2.5 c.c. distilled water 
was added and the tube sterilized in the autoclave (ten minutes at 
