The Air We Breathe 259 



halations, such as sneezing and coughing, may allow bacteria to 

 pass through these masks, but the organisms are reduced in num- 

 ber. The value of masks worn by personnel during influenza 

 epidemics has been questioned by some who feel that viruses are 

 not held back bv gauze traps placed over the mouth and nose. 

 Some good is undoubtedly accomplished, but the limitations should 

 be recognized. 



Fig. 44. Atomizing of droplets into the air by blowing out the last 

 drop from a pipette. (From Johansson, K. R., and Ferris, D. H. Journal 

 of Infectious Diseases, 1946, 78, 241.) 



Recent studies conducted by the United States Public Health 

 Service and other agencies have graphically shown by means of 

 high-speed cameras the occupational hazards involved in pipetting 

 pathogenic organisms. The colored films available on a rental 

 basis will be a revelation to persons engaged in bacteriological 

 work. The aerosol mists that are created by shaking and pipetting 

 are capable of contaminating the air with large numbers of organ- 

 isms unless precautions are taken to reduce the volume of these 



