322 REAGENTS AND PROCESSES 



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After cooling so that it may be handled, the tube is held in the 

 flame close to the bulb, and by constant turning the tube is heated 

 equally on all sides until it becomes so soft that it may be drawn 

 out. This process is accomplished by taking the tube from the 

 flame and pulling on it gently so that it may be drawn out quite 

 long and narrow. The length of the stem of the bulb should be 

 equal to the depth of the vessel from which the nutrient medium 

 is to be drawn into the bulb. The stem may be severed firom the 

 tube by holding it in the flame of the blow-pipe at the proper dis- 

 tance from the bulb, where it will soon become soft enough to 

 be pulled off from the main tube. Then the end of the capillary 

 neck is held in the flame until a bead is formed; in this way the 

 flask is hermetically sealed. To fill the flask with nutrient fluid 

 the neck is sterilized near the end by passing it through a flame, 

 and the head is broken off with sterilized forceps. The bulb is 

 then heated in the flame of an alcohol lamp or Bunsen burner to 

 expand the air. The end of the neck is next quickly dipped into 

 the nutrient fluid, which is forced up the neck into the bulb as the 

 air in this cools. When the bulb is two-thirds full, the neck is 

 withdrawn from the fluid and hermetically sealed in a flame. In 

 filling the bulb the greatest care must be taken to keep the stock 

 of nutrient medium from any source of contamination, if it has 

 once been sterilized. Chemical flasks with narrow necks serve 

 well for a common receptacle. These should be kept stoppered 

 with a cotton plug, and to fill the small flasks the plugs need only 

 to be lifted slightly while the sterilized capillary neck of the 

 small flask is thrust past the plug into the nutrient fluid. If the 

 nutrient fluid is freshly prepared, and has not yet been sterilized, 

 the small flask may be filled, sealed up in the flame, and sterilized 

 in the steam sterilizer or in a vessel of boiling water for an hour 

 each day on three successive days. The nutrient fluid will keep 

 indefinitely in the little flasks, and when a drop is wanted for a 

 drop culture, it is only necessary to sterilize the end of the capil- 

 lary neck in a flame, break off the bead with sterilized forceps, 

 invert the- flask, and place the palm of the hand over the bulb. 

 The heat of the hand will expand the air over the fluid and force 



