BACTERIOLOGICAL EXAMINATION OF AIR. 117 



cubic millimeter by one thousand. Then, as the milk was concentrated 

 twenty times, you divide by 20. (If it were diluted twenty times, 

 you would multiply by 20.) 



Example: Found an average of 50 cells per square millimeter. 

 This would make 500 per cubic millimeter, and 500,000 per c.c.; 

 . then 500,000 divided by 20 would give 25,000. 



|There is no agreement as to a standard for allowable leukocytes. 

 Even in apparently healthy animals they may exceed 100,000 per c.c. 

 Doane has suggested 500,000 per c.c. as a preferable limit. 



The smear methods for determining the number of leukocytes 

 present do not compare in accuracy with the volumetric ones. 



BACTERIOLOGICAL EXAMINATION OF AIR. 



In Paris a cubic meter of. air was found to contain the following 

 number of organisms: 



Suburbs. Winter, 145 moulds, 170 bacteria. 



Summer, 245 moulds, 345 bacteria. 



City Hall. Winter, 1345 moulds, 4305 bacteria. 



Summer, 2500 moulds, 9845 bacteria. 



Air of hospitals, especially after sweeping, may contain 50,000 

 bacteria per cubic meter. There does not seem to be any particular 

 relation between the amount of carbon dioxide in air and the bacterial 

 content. 



Petri's Rough Method. Exposure of a lactose litmus agar plate 

 (capacity 100 sq. cm.) for five minutes will give the number of organ- 

 isms present in ten liters of air. Multiply by 100 for one cubic meter. 



The two groups of organisms usually found in air are (i) bacteria 

 and (2) moulds. Moulds (spores) may be carried by currents of air; 

 bacteria, however, are generally carried about by particles of dust or 

 finely divided liquids (spray). On the lactose litmus agar plate 

 staphylococci and streptococci show as bright red colonies. 



Sedgwick Tucker Sterile Granulated Sugar Method. Sterilize 

 aerobioscope and introduce granulated sugar on support. Again 

 sterilize (not over 120 C. in dry-air sterilizer). Allow a given quan- 

 tity of air to pass through; then shake the sugar into wide part of 



