66 CULTURES AND THEIR STUDY. 



three beef-tea tubes, from each one of which a tube of 

 liquefied gelatin is inoculated. This complicates the work 

 considerably, and errors are also more likely to occur because 

 of the frequent transfer of the material. 



When one tube is fo be inoculated from another, tube No. 1 

 is held between the thumb and first finger of the left hand 

 with the closed end directed toward the back of the hand. 

 Tube No. 2 is held in the same manner between the first and 

 second fingers. The inoculating needle is held in the right 

 hand. The glass handle of the needle should be at least six 



FIG. 20. 



6 



(a) Looped and (b) straight platinum wires in glass handles. 



inches long, and the platinum wire three inches long and of 

 medium thickness. A little loop is made in the free end of 

 the wire. Before inoculating the tubes, the cotton plugs are 

 twisted so that they can be removed easily. The tubes 

 should be held very obliquely, as the air of the laboratory is 

 always laden with germs. When ready to inoculate, sterilize 

 the needle, and with the ring and little fingers of the right 

 hand remove the cotton plug of tube No. 1, take out a loop- 

 ful of material and immediately replace the plug. Now re- 

 move the plug from tube No. 2 as before, pass in the platinum 

 needle, shake gently, withdraw the needle, and replace the 

 plug. Sterilize the needle. The cotton plug is always held 

 between the fingers. It must not be laid on the table even 

 for an instant, because of the possibility of contamination. 

 Holding the plug between the fingers mentioned leaves the 

 hand practically free to perform the inoculation unhampered 

 and without delay, and the plug is safe from contamination. 

 With a little practice, this method can be carried out with con- 

 siderable accuracy and rapidity. Inoculations should not be 



