EXAMINATION OF BACTERIA WITH THE MICROSCOPE. 33 



used constantly in doing bacteriological work. It is the 

 tool by means of which one is able to handle bacteria with 

 impunity. It serves in fact as a kind of additional finger. 

 The platinum 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 

 number 23, American wire gauge (Brown and Sharp). 

 The wire may be straight throughout 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 



Straight platinum wire and platinum wire loop. 



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

 before putting it down, heat it again to a red heat. After 

 the needle has become wet by clipping it in a fluid and is to 

 be sterilized in the flame, it is necessary to avoid " sputter- 

 ing " of the fluid by bringing the wet needle gradually to 

 the flame, so as to dry the material adhering to it before 

 burning it. This procedure must be done with great care 

 when the wire has been dipped in milk 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 



