AIR 135 



antagonism to harmful bacteria, would be destroyed by pasteurization, (2) the more 

 rapid development of bacteria in milk that has been pasteurized (3) interference with 

 nutritive qualities and (4) pasteurized milk does not show its deterioration as does 

 unpasteurized milk, thus failing to give a clue as to the age of the milk. 



The United States Bureau of Animal Industry in studying this important phase 

 of the milk question has grouped the milk bacteria into three classes (a) acid -forming, 

 (b) putrefactive (liquefying) and (c) inert bacteria. In their investigations it was 

 found that many acid- forming bacteria withstood temperature as high as 168 F., 

 so that pasteurized milk was soured just as is raw milk, but more slowly. They found 

 that pasteurized milk showed fewer putrefactive bacteria than raw milk, so that 

 even should it be a fact that injurious toxins were produced by spore-bearing putre- 

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

 rized milk. 



The statement so often advanced that bacteria develop more rapidly in pasteu- 

 rized milk than in raw milk was proved fallacious. 



It was recommended that holding the milk for thirty minutes at 145 F. was a 

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

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

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



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 organisms 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 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 



