THE MICROBIOLOGY OF THE ATMOSPHERE 



are cheapness and portability; time-discrimination is accurate to seconds 

 if desired; it is suitable for work in the less accessible places and for short- 

 time samples (5-10 min.). However, it is fatiguing to use, and being 

 unsuitable for continuous operation, it cannot conveniently be used to 



STAGE NO. 

 JET SIZE 

 JET VELOCITY 



STAGE 1 

 0.0465" DIA. 

 3.54 FT/SEC 



STAGE 2 

 0.0360" DIA. 

 5.89 FT/SEC 



STAGE 3 

 0.0280" DIA. 

 9.74 FT/SEC 



STAGE 4 

 0.0210" DIA. 

 17.31 FT/SEC 



STAGE 5 

 0.0135" DIA. 

 41.92 FT/SEC 



STAGE 6 

 0.0100" DIA. 

 76.40 FT/SEC 



^^-^^^^^-^-^^^-^ W^/////////>>^^ 



Fig. 18. — Diagram of six-stage Andersen sampler. (Reproduced by permission of Dr. 

 Ariel A. Andersen from the journal of Bacteriology, 76, 1958.) 



trace diurnal or weather effects on the air-spora. Brook (1959) has devel- 

 oped essentially similar equipment for sampling the air-spora of pastures 

 in New Zealand. 



A desirable development of both the Hirst trap and the Portable trap 

 would be versions which presented the catch in a form suitable for culture 

 as an alternative to visual microscopic identification. 



(xi) The Andersen Sampler can be regarded as a development of the 

 so-called 'sieve device' of duBuy & Crisp (1944). In principle this sampler 



102 



