I50 



Methods of Observing Micro-organisms 



Bunsen flame until it becomes greenish-yellow. The hot glass must 

 then be slowly elevated above the flame, so as to allow it to anneal. 

 This manceuver removes the organic matter by combustion. It is 

 not expedient to use covers twice for bacteriologic work, though if 



well cleansed by immersion 

 in acid and washing, they 

 may subsequently be em- 

 ployed for ordinary micro- 

 scopic objects. 



The fragility of the 

 covers and their likeli- 

 hood to be broken or 

 dropped at the critical mo- 

 ment, make most workers 

 prefer to stain directly upon 

 the slide. The slide should 

 be thoroughly cleaned, and 

 if the material to be ex- 

 amined is spread near one 

 end, the other may serve 

 as a convenient handle. 

 The slide is also to be 

 preferred if a number of 

 examinations are to be 

 made simultaneously or 

 for comparison, as it is 

 large enough to contain a 

 number of "smears." 



SimpleMethod of Stain- 

 ing. — The material to be 

 examined must be spread 

 in the thinnest possible 



Fig. 26. — Apparatus for keeping objects 

 under microscopic examination at constant 

 temperatures (Nuttall). 



layer upon the surface of 

 the perfectly clean cover- 

 glass or sUde and dried. The most convenient method of 

 spreading is to place a minute drop on the glass with a platinum 

 loop, and then spread it evenly over the glass with the flat wire. 

 Should it be stained at once it would all wash off, so it must next 

 be fixed to the glass by being passed three times through aflame, 

 experience having shown that when drawn through the flame three 

 times the desired effect is usually accomplished. The Germans 

 recommend that a Bunsen burner or a large alcohol lamp be used, 

 that the arm describe a circle a foot in diameter, each revolution 

 occupying a second time, and the glass being made to pass through 

 the flame from apex to base three times. This is supposed to be 

 exactly the requisite amount of heating. The rule is a good one for 

 the inexperienced. 



