NUTRIENT MEDIA AND METHODS OF CULTIVATION. 109 



the fourth anci fifth fingers of the left. Remove the plug of the 

 other tube in the same way, placing it between the third and fourth 

 fingers of the left hand. With the needle take up a droplet of the 

 cultivation and stir it round in the liquefied jelly. Replace the plugs, 

 and set aside the cultivation. Hold the freshly inoculated tube be- 

 tween the index finger and thumb of either hand, almost horizontally, 

 then raise it to the vertical, so that the liquid gelatine gently flows 

 back. By repeating this motion and rolling the tube between the 

 fingers and thumbs the micro-organisms which have been introduced 

 are distributed throughout the gelatine. Any violent shaking, and 

 consequent formation of bubbles, must be carefully avoided. From 

 the inoculated tube, in the same manner inoculate a fresh tube of 

 liquefied gelatine, introducing into it three droplets with a sterilised 

 needle. After tilting and rolling this tube, as in the previous case, 

 the same process is repeated with a third tube, which is inoculated 

 from the second tube. This last tube must be inoculated in different 

 ways, according to experience, for different micro-organisms. Some- 

 times a sufficient separation of the micro-organisms is attained by 

 inoculating the last tube with a straight, instead of a looped, needle, 

 dipping it from the one into the other from three to five times. 



The next process consists in pouring out the' gelatine on glass 

 plates and allowing it to solidify. 



Preparation of the Gelatine- Plates. — The directions to be observed 

 in pouring out the gelatine are as follows : — 



Place the box containing sterilised plates horizontally, and so 

 that the cover projects beyond the edge of the table ; remove the 

 cover, and withdraw a plate with sterilised forceps ; hold it between 

 the finger and thumb by opposite margins, rapidly transfer it to 

 the filter-paper under the bell-glass, and quickly replace the cover 

 of the box. On removing the plug from the tube which was first 

 inoculated, an assistant raises the bell-glass, and the contents of the 

 tube are poured on to the plate ; with a glass rod the gelatine must 

 be then i-apidly spread out in an even layer within about half an 

 inch of the margin of the plate. The assistant replaces the bell- 

 glass, and the gelatine is left to set. Meanwhile a glass bench or 

 metallic shelf is placed in the damp chamber, ready for the reception 

 of the plate-cultivation, and when the gelatine is quite solid the 

 plate is quickly transferred from under the bell-glass to the damp 

 chamber ; precisely the same process is repeated with the other 

 tubes, and the damp chamber, labelled with the details of the 

 experiment, is set aside for the colonies to develop. Not only plate- 

 cultures should be carefully labelled with date and description, but 



