BY R. GREIG-SMITH. 



221 



Previous to spotting the cover-glass, the moist chamber has 

 been prepared by passing a metal or glass ring, 1 cm. deep, 

 through the flame, painting the lower end with vaseline, and 

 placing it in the centre of a glass-slide. As the ring cools, the 

 vaseline sets and forms a firm junction. In hot weather, the 

 ring is dipped into solid beeswax, withdrawn with the adhermg 

 molten wax, and placed on the slide. The sterilisation of the 

 slide is rarely necessary. A drop of water is introduced by 

 means of a capillary pipette, such as is used in opsonic work, 

 and a clean cover-glass is flamed and placed upon the top of the 

 ring. The chamber is taken as being stei'ile. The cover-glass 

 is spotted with the yeast-suspension, the ring of the chamber is 

 painted with vaseline, and the cover-glass inverted and pressed 

 down. The preparation is then examined, and the drops con- 

 taining a single cell noted. It is rarely necessary to examine 

 the droplets before fixing the slide to the ring, when the method 

 of preparing the suspension, which I am about to descril)e, is 

 followed. 



The method is that used by Sir A. E. Wright* for the dilution 

 of microbic fluids. A wide capillary pipette is prepared by 

 heating a six-inch length of glass-tubing of 4 mm. bore until 

 soft, in the flame of a wing-attachment of the bunsen, and draw- 

 ing the whole to twelve inches. When cold, it is cut across the 

 middle, and blind teats are attached to the broad ends of the 

 two pipettes. The pipette is marked with a blue pencil at 1 

 inch from the point. A more or less milky suspension of yeast 

 cells is drawn up to the mark, then an air-bubble is drawn up, 

 then a length of sterile nutritive medium, such as wort, then 

 another air-bubble followed by a length of medium. '1 hus we 

 have an inch of the charge, of the first and second dilutions, 

 each separated by an air-bubble. The second dilution is gently 

 blown upon a sterile glass-slide, and is used for spotting the 

 cover-glasses with the capillary. The remarkable point about this 

 method of dilution is that, however opalescent the original sus- 

 pension of cells may be, the second dilution contains them in so 



*Brit. Med. Journ., Oct. 30th, 1915, p.633. 



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