112 BACTERIOLOGY 



of the wire from the first tube to the second. When the needle 

 is introduced into or removed from either tube it should not touch 

 the side of the tube at any point,and should only come in contact 

 with the region desired. After inoculation of the second tube 

 has been effected, the wire is heated to redness in the flame, the 

 necks of the tubes are passed through the flame, and the plugs are 

 returned to their respective tubes. In the same manner transfer 

 three loopfuls from tube No. 2 into tube No. 3. The original 

 material will obviously be diluted in tube No. i , more in tube No. 2, 

 and still more in tube No. 3. The most convenient form of plate 

 is that known as a Petri dish, a small glass dish about 10 cm. in 

 diameter and 1.5 cm. in height, provided with a cover which is 

 a little larger but of the same form. This dish should be cleaned, 



Pig. 42. — Petri dish. 



dried and sterilized for an hour in a hot-air sterilizer at 150° C. 

 or higher. When it is cool it may be used. 



Such dishes having previously been prepared, the contents of 

 tube No. I are poured into one dish, and those of tube No. 2 

 into another, and those of tube No. 3 into a third. They are 

 labeled Nos. i, 2, and 3.^ In pouring proceed as follows: re- 

 move the plug of tube No. i ; heat the neck of the tube in the 

 flame; allow it to cool, holding it in a nearly horizontal position. 

 When the tube has cooled, Uft the cover of the Petri dish a little, 

 holding it over the dish; pour the contents of tube No. i into the 

 dish, and replace the cover. The interior of the dish should be 

 exposed as Uttle and as short a time as possible. Tubes Nos. 2 and 

 3 are to be treated in the same manner. Burn the plugs, and 



' The labels should be moistened with the finger, which has been dipped in water. 

 They should not be licked with the tongue. While working in the bacteriological 

 laboratory it is best to make it a rule that no object is to be put in the mouth. 



