22 MANUAL OF BACTERIOLOGY. 



wire must be stiff enough not to bend too easily, and yet it 

 should not be so large that it will not cool rapidly after heating. 

 A good size for most purposes is No. 23, American wire 

 gauge (Brown & Sharp). The wire may be straight through- 

 out its length, or the tip may be bent to form a loop (German, 

 Oese). It is well to follow, from the beginning, certain rules 

 which make the use of the platinum wire safe and accurate. 

 Every time it is taken into the hand and before using it for any 

 manipulation heat it in the flame of a Bunsen burner or an 

 alcohol lamp to a red heat; and always, after using, and before 

 putting it down, heat it again to a red heat. If the needle is wet 

 it should be dried by holding it near the flame in order to avoid 



c- 



FlG. 5. — Straight platinum wire and platinum loop. 



the "sputtering" which occurs if it is plunged at once into the 

 flame. This precaution is especially called for when the wire 

 has been dipped in mflk or other substances containing oil. 

 When the needle "sputters," as it is called, from too rapid 

 heating, particles that have not yet been sterilized may be 

 thrown some distance. On no account should the needle 

 touch any object other than that which it is intended it should 

 touch. With such a platinum wire, which has been properly 

 sterilized, one can easfly remove portions from a culture of 

 bacteria, or from a fluid in which bacteria are supposed to be 

 present. The glass rod in which the platinum wire is fixed 

 should be held between the thumb and forefinger of the right 

 hand like a pen. (For the manner of holding test-tubes, see 

 page 79.) 



