MIQUEDS METHOD 



103 



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by the orifice c, the two asbestos plugs are fitted in position, each 

 tube wrapped in a piece of wrapping paper and 

 sterilised in the hot air steriliser for one hour at 

 1 50° C. The paper will act as a further protection 

 against possible contamination of the tube before 

 it is required for use. Thus furnished, the tubes 

 can be carried without risk in the pocket or else- 

 where. 



When required for use the paper covering is 

 removed, the tube placed in a position approach- 

 ing the vertical ; the plug d is removed, and the 

 extremity of the tube joined up to the india-rubber 

 tubing of an aspirating apparatus. One or two 

 smart taps of the finger are then given to the 

 tube in order to bring the salt particles into close 

 contact, the plug c is removed, and the aspirating 

 apparatus set in action. After a given quantity 

 of air has passed through the tube, the plug ^, 

 which should in the meantime have been carefully 

 protected from contamination, is replaced, the tube 

 itself detached from the aspirating apparatus, and 

 conveyed to the laboratory for examination. As 

 many tubes as thought desirable can be employed, 

 either as controls or for the examination of the 

 air in different localities. As the organisms are 

 deposited upon the particles of an inert salt in a 

 dry condition, the necessity of immediate exami- 

 nation is not so great as in the case of other 

 methods. 



On arriving at the laboratory, the end of the 

 tube containing the sulphate of soda is lightly 

 passed through the Bunsen flame, the plug c with- 

 drawn, and the contents allowed to fall into a tube 

 containing 10 c.c. of bouillon. The tube should be 

 well rolled in the hand to ensure dissolution of the 

 soda and a general distribution of the organisms 

 in the medium, and given quantities withdrawn by 

 means of a sterile calibrated pipette, and distri- 

 buted into tubes of gelatine, from which plate 

 cultivations are made in the ordinar>' manner. 

 The plates are left for three days or longer at 

 room temperature, and an enumeration is then made of the colonies 



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Fig. 30. — Air-filter- 

 ing tube ; actual 

 size. 



