BACTERIOLOGY OF AIR 



159 



factive organisms the development of such organisms would be even less in pasteur- 

 ized milk. 



The statement so often advanced that bacteria develop more rapidly in pasteurized 

 milk than in raw milk was proved fallacious. 



It was recommended that holding the milk for thirty minutes at i45F. was a far 

 better method of pasteurizing than quickly bringing the milk to a temperature of 

 i85F. (flash method). All admit the great value of the killing of important patho- 

 gens (typhoid, cholera, streptococci, etc.). 



BACTERIOLOGICAL EXAMINATION or AIR 



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

 number of organisms: 



Suburbs. Winter, 



Summer, 



City Hall. Winter, 

 Summer, 



145 moulds, 



245 moulds, 



1345 moulds, 



2500 moulds, 



170 bacteria. 



345 bacteria. 

 4305 bacteria. 

 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 organisms present in 10 liters of air. 

 Multiply by 100 for i^cu. m. 



FIG. 44. Sedgwick -Tucker aerobiscope. (Mac Neat.) 



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 i2oC. in 

 dry-air sterilizer). Allow a given quantity of air to pass through; then shake the 

 sugar into wide part of aerobioscope. Now pour in 10 or 15 c.c. of melted gelatin 

 (40 C.) to dissolve sugar. Roll tubes as for Esmarch roll cultures, and incubate 

 at room temperature. To draw air through the aerobioscope, connect the small end 

 with a piece of rubber tubing which is attached to a tube in the stopper of an aspirat- 

 ing bottle. Having poured a definite quantity of water into the aspirating bottle, 



