v] METHODS OF INOCULATION 83 



of water can hereby be subjected to examination, otherwise 

 ordinary gelatine plate-cultivations must be relied upon, 

 Eut since for these only small quantities of the water can be 

 used, the former method is far preferable, as by the ordinary 

 gelatine plate method the proteus could be detected only if 

 present very freely. 



Examination of Air. — Miquel, Hesse, P. Frankland, 

 Carnelly, Robertson, and others have investigated the 

 number of microbes present in various samples of aii-, 

 under various conditions (town air, country air, mountain 

 air, air of schools, dwelling rooms, hospitals, &c.). The 

 method is always in principle this : by means of an ordin- 

 ary gas clock or gasometer a measured quantity of air is 

 drawn at a moderate rate by means of an aspirator — fall 

 cf water or mercury — through a cylindrical tube (Hesse), 

 or through a flask (Frankland, Carnelly) containing a 

 thin layer of solidified nutrient gelatine. Hesse's tubes 

 are cylindrical, in which nutrient gelatine while still liquid 

 has, by slightly rolling the tubes, set at one side in a 

 thin film ; they are plugged at each end with a sterile india- 

 rubber stopper containing a sterile glass tube ; to each is 

 fixed a sterile tube, one is connected during the experiment 

 with the gas clock, the other with the aspirator ; the time 

 during, or the rapidity with which the air is drawn through 

 and the amount of air so drawn through are accurately 

 noticed ; after the experiment the glass tubes are plugged 

 with cotton wool so as to serve as a filter against the 

 entrance of further microbes. In Dr. P. Frankland's ex- 

 periments, the air is passed through a sterile plug (asbestos 

 or glass wool) contained in a tube or flask, and this having 

 retained all microbes is then thrown into the gelatine ; this 

 is liquefied and well shaken so as to wash out of the plug 

 all microbes and to uniformly distribute them in the gelatine. 



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