SIMPLE STAINING 



55 



as there described. If, however, the growth is upon solid media, 



the following method should be adopted : — 



Place a small droplet of distilled water in the centre of a 

 thoroughly clean slide. With the point of a fine platinum needle 

 take up a trace of the culture under examination and inoculate 

 with it the water on the slide. Spread the droplet, which now 

 ought to have a cloudy appearance, in a thin even film by 

 gently moving the needle in a circular direction. Dry by waving 

 the slide to and fro in the heated air above a Bunsen burner or 

 spirit lamp. A well-spread film should have the appearance of a 

 thin opaque cloud of even density, just visible on the surface of the 

 slide. 



Fixation. — The object of fixing is to coagulate the albuminous 

 material and cause perfect adhesion of the prepared film to the 

 slide. The following alternative methods are recommended : — 



{a) Heat. — Holding the glass slide by one extremity between 

 the thumb and index finger of the right hand, pass it, film side 

 upwards, gently through the flame three times, allowing the under 

 surface to rest on the back of the left hand between each passage. 

 The judging of the exact amount of heat required is a matter of 

 practice, but it should on no account be greater than the back of 

 the hand can comfortably bear when the under surface of the slide 

 is placed upon it. 



{V) Alcolwl-etJier. — Place one or two drops of a mixture of equal 

 parts of absolute alcohol and ether upon the dried film, and allow 

 it to evaporate. 



{c) Fonnol-alcoJiol. — Formalin i part, absolute alcohol 9 parts. 

 Leave in contact for from three to four minutes, wash well in 

 water, blot off" excess of moisture, and stain. 



id) Perchloride of mercury. — Saturated aqueous solution. 

 Leave in contact with the film for from four to five minutes. 

 Wash off" with a stream of water and apply Gram's iodine solution 

 in order to dissolve out any formed crystals of the salt. Wash 

 again in water, blot off" excess of moisture, and apply stain. This 

 fixing agent should be used on all occasions when dealing with 

 morbid material or cultures of a specially virulent nature. 



Simple Staining- of Milk Specimens 



The ordinary methods of staining bacteria in use in the 

 laboratory may be readily applied in the case of milk. In certain 



