364 



PUBLIC HEALTH BACTERIOLOGY 



5. Sedgwick and Tucker's Method. A specially shaped 

 tube is used, in which are placed cotton plugs (3), and cane 

 sugar is packed into a narrow part of the tube. One plug 

 is removed, and air aspirated through the sugar (the whole 

 apparatus having been previously sterilized at 120 C.). 

 The plug is then replaced, the sugar is shaken down into 

 a wider part of the tube, and liquid gelatin is poured in. 

 The sugar melts into the gelatin, and a roll culture is 

 made before the latter solidifies. Incubate at 22 C. and 

 count colonies daily. 



Organisms found. Yeasts, Spores of moulds, Strepto- 

 coccus brevis, B. coli, B. mycoides, B. enteritidis sporogenes, 

 Streptococcus epidermidis, Streptococcus salivarius. 



The last two serve to indicate pollution by particles of 

 skin and saliva. The preceding ones indicate pollution 

 by dirt from the street, brought in on the boots, if the 

 air tested is that of a room ; or it may be blown in. 



The effect of stirring dust is to increase the ratio of 

 bacteria to moulds, whereas in still air, bacteria settle 

 down much more rapidly than moulds. The purer the 

 air, the more nearly do the numbers of the bacteria and 

 of the moulds approximate. This is well shown in the 

 figures found by the examination of i cubic metre of air 

 (1000 litres or 220 gallons), taken in Paris and the suburbs, 

 in the various seasons. 



Particulate pollution of the air by material from the 

 upper respiratory passages from the skin and from the 

 street may all be detected by exposing plates filled with 

 broth to the air for a definite time ; incubating anaerobi- 

 cally for forty-eight hours at 37 C., and examining for 

 certain test organisms. (Gordon.) 



