60 METHODS OF CULTIVATION OF BACTERIA. 



b. Shake b and transfer two loops to c. The plugs of the 

 tubes are in each case replaced and the tubes returned 

 to the beaker. The hands having been washed in 

 perchloride of mercury i-iooo and dried, the plate 

 box is opened, and a plate lifted by its opposite edges and 

 transferred to the levelled ground glass (as in Fig. 19). 

 The plug of tube a is now removed and the mouth of the 

 tube passed two or three times through the Bunsen flame, 

 the tube being meantime rotated round a longitudinal axis. 

 Any organisms on its rim are thus killed. The bell jar of 

 the leveller being now lifted a little, the gelatine is poured 

 out on the surface of the sterile plate, and while still fluid, 

 is spread by stroking with the rim of the tube. The 

 plate is now transferred to the moist chamber as rapidly as 

 possible, so as to avoid atmospheric contamination. To do 

 this, one of the benches is put on the top of the chamber. 

 The top is then lifted off and placed on the table near the 

 leveller. The plate is then quickly transferred to the 

 bench. The latter is lifted by its ends and placed at the 

 bottom of the moist chamber, the top of which is now 

 replaced. Tubes b and c are similarly treated, and the 

 resulting plates stacked in series on the top of a. The 

 chamber is labelled and set aside for a few days till the 

 appearance of the colonies as little grey or coloured points 

 on the plates, indicates that growth has taken place. Very 

 often from such naked-eye appearances as colour, contour, 

 shape, liquefaction or non- liquefaction of the gelatine, 

 these colonies can be classified into groups. Further aid 

 is obtained by examination with a magnifying glass or a 

 low-power microscopic lens. Their character is ultimately 

 settled by making film preparations for examination with 

 higher powers. During this process of classifying the 

 colonies, the plate must be kept covered in the moist 

 chamber as much as possible. When the grouping 

 is completed, gelatine tubes are inoculated from a 

 colony of each group, and the different organisms 

 present capable of growing on gelatine, are thus separ- 

 ated. The cultures obtained can then be investigated, 



