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Dr. T. Cainelley and Mr. T. Wilson. 



(2.) It gives accurate results, as shown by comparative tests. 



(3.) There is no risk of aerial contamination either during the 

 preparation of the flasks previous to use, or subsequently during the 

 growth of the colonies. 



(4.) It is very much cheaper than Hesse's method, for a flask fitted 

 ready for use costs only about Is. 3d. (exclusive of jelly), where a 

 Hesse's tube costs about 3s. This is a very material item when a 

 large number of experiments are to be made. 



(5.) The flasks being of thin glass very rarely break during sterili- 

 sation, whereas this is a serious source of annoyance and expense 

 in the case of Hesse's tubes. 



(6.) There is not the least chance of leakage during sterilisation, 

 as sometimes occurs with Hesse's tubes, for in the latter method the 

 india-rubber caps have to be very carefully fitted on, since with the 

 slightest crease in the india-rubber the tubes are sure to leak during 

 sterilisation, with consequent loss of jelly, which entails refitting and 

 refilling. 



(7.) There is a great saving in jelly. A flask needs only 10 c.c, or 

 one-fifth the quantity required by a Hesse tube. In a long series of 

 experiments the cost of jelly is very considerable, both in the expense 

 of the materials and the time required to make it. 



(8.) In common with Frankland's process the flask method is free 

 from errors arising from " aerial currents," which are sometimes so 

 serious a source of error in Hesse's tubes when employed for deter- 

 minations in outside air, such currents being apt to blow micro- 

 organisms into a Hesse tube over and above those contained in the 

 volume of air aspirated. 



(9.) An advantage which the flask method possesses over Frank- 

 land's process is that in the former the micro-organisms pass directly 

 on to the nutrient jelly in the flask, whereas in the latter they are first 

 entangled in the glass-wool filter, and afterwards transferred to the 

 cultivating medium, when they are disentangled from the glass-wool 

 by agitation with the jelly, an operation which would seem to require 

 considerable care. Again, in Frankland's process the micro-organisms 

 are embedded in the mass of the jelly, while in our method they fall 

 and grow directly on the surface. 



(10.) On the other hand Frankland's method possesses two import- 

 ant advantages ; first, on account of the small size of his filter tubes, 

 they admit of being carried from place to place without inconvenience, 

 whereas flasks and Hesse tubes are comparatively bulky. This is a 

 great point when a large number of determinations are to be made at 

 different places away from the laboratory. Second, the air can be 

 aspirated through one of Frankland's filters about four times as fast 

 as through a Hesse's tube, which is of considerable advantage in the 

 case of determinations in outside air, where at least 10 litres require 



