90 CLINICAL BACTERIOLOGY. 



closed with a cotton stopper. The culture-medium could 

 now be poured upon a plate for solidification, but this is 

 usually not done at this time, because, as a rule, the first 

 gelatin-tube, or, as it is called, the original tube, contains 

 too large a number of bacteria, whose colonies would there- 

 fore develop too closely together upon the plate. For this 

 reason a first an(i a second dilution are yet prepared. To 

 this end the inoculated original tube is taken between the 

 thumb and the index-finger of the left hand, another gela- 

 tin-tube, liquefied at 40 C. (104 F.), is held between the 

 index-finger and the middle finger, and the cotton stoppers 



Fig. 20. Manner of holding tubes during inoculation : a, Original tube ; 6, tube to 

 be inoculated ; c, cotton plugs. 



are removed, the first being held between the middle and the 

 ring finger, and the second between the ring and the little 

 finger. Then, with the platinum needle sterilized by heat, 

 three loopfuls of the liquid contents of the original tube 

 are successively taken from the original tube and intro- 

 duced into the second gelatin -tube (first dilution). (Fig. 20.) 

 After vigorous shaking, in the manner described, of the 

 tubes, now again closed, a third tube of liquefied gelatin is 

 inoculated in an identical manner with three loopfuls of the 

 first dilution (second dilution). 



Rectangular plates of glass will meanwhile have been 

 sterilized in sheet-iron boxes (plate-pockets) in the hot-air 



