3 I2 



METHODS OF IDENTIFICATION AND STUDY 



3. Prepare a similar series of tube cultivations 

 numbered consecutively 13 to 18 and add varying 

 quantities of the formaldehyde solution, viz. : 



To tube No. 13 add i.o c.c. (=1:1,000) 

 To tube No. 14 add 0.4 c.c. (= 1 12,500) 

 To tube No. 15 add 0.2 c.c. (= 1 15,000) 

 To tube No. 16 add o.i c.c. (=1:10,000) 

 To tube No. 17 add 0.075 c.c. (= i : 15,000) 

 To tube No. 18 add 0.05 c.c. (=1:20,000) 



4. Incubate all three sets of cultivations under' opti- 

 mum conditions as to temperature and atmosphere. 



5. Examine each of the culture tubes from day to 

 day, until the completion of seven days, and note 

 those tubes, if any, in which growth takes place. 



6. From such tubes as show growth prepare sub- 

 cultivations upon suitable media, and ascertain that 

 the organism causing the growth is the one orig- 

 inally employed in the test and not an accidental 

 contamination. 



Inferior Lethal Coefficient. 



Apparatus Required: 



Highly concentrated solutions of the disinfectants. 



Sterile test-tubes in which to make dilutions from the concen- 

 trated solutions of the disinfectants. 



Hanging-drop slides. 



Cover-slips. 



Erlenmeyer flask containing 100 c.c. sterile distilled water. 



Case of sterile pipettes, 10 c.c. (in tenths of a cubic centimetre). 



Case of sterile pipettes, i c.c. (in tenths of a cubic centimetre). 



METHOD. 



1. Prepare a surface cultivation of the "test" 

 organism B. anthracis upon nutrient agar in a culture 

 bottle and incubate under optimum conditions for 

 twenty-four hours ; then examine the cultivation micro- 

 scopically to determine the absence of spores. 



2. Prepare solutions of different percentages of each 

 disinfectant. 



3. Make a series of hanging-drop preparations from 



