32 



BACTERIQLOGY 



Q 



The Platintmi Wire.— The substance under examination 

 is placed upon thin slips of glass called cover-glasses or directly 

 upon thicker strips of glass, called slides. The material is spread 

 over the glass by means of a platinum wire which has been fixed 

 in a glass rod about six inches long. Such a platinum wire is used 

 constantly in doing bacteriological work. 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 No. 28, English standard 

 gauge, diameter .014 inch. Instead of the expen- 

 sive platinum wire, one may use nichrome wire, 

 which is much cheaper and serves as well for all 

 ordinary purposes. The wire may be straight 

 throughout its length, or the tip may be bent to 

 form a loop. It is well to follow, from the begin- 

 ning, certain rules which make the use of the 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. After, the needle has become wet by 

 dipping it in a fluid and is to be sterilized in the 

 flame, it is necessary to avoid "sputtering" of the 

 fluid by bringing the wet needle gradually to the 

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

 or, -better, by holding it within the central cooler cone of the 

 Bunsen flame to accomplish the same purpose. 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 

 ha:ve 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 



Pig. 20. — Need- 

 les used for inocu- 

 lating media. 



