470 BACTERIOLOGICAL ANALYSES 



8. Liquefy three tubes of nutrient gelatine and add 

 to them 0.5 c.c., 0.3 c.c., and 0.2 c.c., respectively, of 

 the water from the flask, by means of a sterile gradu- 

 ated pipette, as in the quantitative examination of 

 water. Pour plates. 



9. Pour a second similar set of gelatine plates. 



10. Incubate both sets of plates at 20 C. 



11. Enumerate the colonies present in the two sets 

 of gelatine plates after three, four, or five days and 

 average the results from the numbers so obtained; 

 estimate the number of micro-organisms present in 

 i c.c., and then in the 50 c.c. of broth in the flask. 



1 2 . The result of air examination is usually expressed 

 as the number of bacteria present per cubic metre 

 (i. e. t kilolitre) of air; and as the number of organisms 

 present in the 50 c.c. water only represent those con- 

 tained in 10 litres of air, the resulting figure must be 

 multiplied by 100. 



Qualitative. 



1. Proceed exactly as in the quantitative examina- 

 tion of air (vide supra), steps i to 10. 



2. Pour plates of wort agar with similar quantities 

 of the air-infected water, and incubate at 37 C. 



3. Pour plates of nutrient agar with similar quan- 

 tities of the water and incubate at 37 C. 



4. Pour similar plates of wort gelatine and incubate 

 at 20 C. 



5. Pick off the individual colonies that appear in 

 the several plates, subcultivate them on the various 

 media, and identify them. 



EXAMINATION OF SOIL. 



The bacteriological examination of soil yields in- 

 formation of value to the sanitarian during the pro- 

 gress of the process of homogenisation of "made soil" 

 (e. g., a dumping area for the refuse of town) and 



