GELATIN AND POTATO MEDIA. 173 



The platinum wires are sterilized by holding- them in 

 the flame, till incandescent. The end of the glass rod 

 should always be thoroughly heated, and, if any organic 

 matter is present, such as gelatin, it should be burned off. 

 The wires should be kept in a conical test-glass (Fig. 43), 

 in the bottom of which is some cotton. 



FIG. 29. The inoculation of a single tube. 



Place three of the sterilized, gelatin tubes in a water- 

 bath which has been warmed to about 30-35. When the 

 gelatin melts, the tubes are ready for inoculation. With a 

 sterilized, cooled platinum wire, pick up a minute amount, 

 of the growth on potato, of the Bacillus prodigiosus. Place 

 one of the liquefied g'elatin tubes between the thumb and 

 index finger of the left hand, so that it is almost horizontal. 

 It is held in this position in order to prevent foreign matter 

 from dropping into the tube. The neck of the tube with its 

 plug, as well as the palm of the left hand, is turned to the 

 right. In this position the entire length of the tube is be- 

 fore one's eyes (Fig. 29). While still holding the platinum 

 wire in the right hand, grasp the cotton plug with the little 

 finger of that hand, and, remove it by slight rotation. If 

 any tufts of cotton are adherent to the neck of the tube, 

 touch it for a moment to a Bunsen flame. Otherwise, the 

 platinum wire might carry in some of this material, and 

 thus cause unnecessary contamination. As a matter of rou- 

 tine, it is well to always flame the 'neck of a tube before insert- 



