84 BACTERIOLOGY. 



platinum wire till it is white hot in every part, and heating also 

 as much of the glass rod as is made to enter the test-tube, must 

 be carried out with scrupulous care. Indeed it is a good plan to 



FIG. 26. INOCULATING NEEDLES. 



let it become a/orce of habit to sterilise the needle before and after 

 use on every occasion, whatever may be the purposes for which it 

 is employed. 



UNSTAINED BACTERIA. 



The bacteria in liquids, such as pus, blood, and culture- fluids, can 

 be investigated in the unstained condition by transferring a drop with 

 a, looped platinum needle or a capillary pipette to a slide, covering 

 it with a clean cover-glass, and examining without further treat- 

 ment. If it is desirable to keep the specimen under prolonged 

 observation, a drop of sterilised water or salt solution must be run in 

 at the margin of the cover-glass to counteract the tendency to dry. 



Cultures on solid media can be examined by transferring a small 

 portion with a sterilised needle to a drop of sterilised water on a 

 slide, thinning it out, and covering with a cover-glass as already 

 described. 



Tissues in the fresh state may be teased out with needles in 

 sterilised salt solution, and pressed out into a sufficiently thin layer 

 between the slide and cover-glass. Glycerine may in many cases 

 be substituted for salt solution, especially for the examination of 

 micro-organisms such as Actinomyces and mould fungi. 



There is, as a rule, no difficulty in recognising the larger micro- 

 organisms such as those just mentioned; but when we have to 

 deal with very small bacilli and micrococci, they may possibly be 

 mistaken for granular detritus or fat-crystals, or vice versa. They 

 are distinguished by the fact that fatty and albuminous granules 

 are altered or dispersed by acetic acid, and changed by solution 

 of potash ; alcohol, chloroform, and ether dissolve out fat-crystals 



