METHOD OF STRA USS 107 



kept liquid throughout the operation, either by being placed in a 

 beaker of warm water, or more simply by being held in the hand. 

 The lateral tube is connected up with the aspirator, the cotton- 

 wool plug removed from the orifice of entry, and the aspirator put 

 in action. The aspired air passes through the central tube and 

 bubbles through the gelatine, leaving behind it the greater pro- 

 portion of the organisms contained therein. Excessive frothing 

 is prevented by the thin coat of oil on the surface of the gelatine. 

 Such organisms as may pass through the gelatine are either 

 deposited in the tube itself, or caught by the lower glass wool plug 

 in the lateral branch. 



As soon as the required quantity of air has been passed through, 

 the apparatus is detached, and by careful aspiration the liquid 

 gelatine is drawn several times up into the pipette tube, in order 

 to wash from its walls any organisms which may have remained in 

 it. The glass wool plug above the constriction in the lateral branch 

 is removed, and by means of a sterile needle or fine glass rod, the 

 one below it is pushed forward and allowed to fall into the melted 

 gelatine. The upper plug is then replaced, and the tube is well 

 rolled in the hand and agitated in order to secure an even distribu- 

 tion of the organisms in the gelatine. Petri dish cultivations are 

 then made in the ordinary manner, by means of the pipette tube, 

 or, if preferred, this latter is withdrawn, and an Esmarck roll culture 

 made upon the inner walls of the larger tube itself. 



5. Miquel's flask method — 



This method has been discarded by its originator in favour of 

 the system of soluble filters. It consists in the aspiration of a 

 given volume of air through 30 c.c. of sterile water or bouillon con- 

 tained in a special flask. After aspiration the water or bouillon 

 is distributed into a large number of ordinary flasks of sterile 

 bouillon, from 30 to 50 at least. Calculation of the organisms 

 present is made by noting proportion of flasks remaining non-turbid 

 after incubation, it being presumed that each flask in which growth 

 takes place contains but a single germ. The large number of 

 flasks in use for a single operation, and the fact that, however great 

 the fractioning, the possibility always arose that more than one 

 organism would find its way into a certain proportion of the flasks, 

 led to the discontinuance of this method. 



6. Hesse's method— 



In this method a given volume of air is caused to circulate 

 in and pass through a glass tube, the interior walls of which are 



