26 GENERAL BACTERIOLOGY LESSON 



Place the former in the water incubator at 42 -5 C., 

 and keep the latter at 38 C. 



Compare them after forty-eight to eighty hours and 

 notice the difference in the tint of the litmus. The 

 latter or more virulent culture decolourises the 

 agar-agar more rapidly. 



Impression Specimens 



(a) Examine the sloped gelatine tubes (vide Lesson Y. 7, 

 p. 23) with a magnify ing -glass for colonies of anthrax 

 bacilli. 



(b) If found, rapidly dip the gelatine tube into boiling 

 water, having previously removed the cotton-wool plug. 

 This momentary heating will free the gelatine from the 

 sides of the tube. 



(c) Slide the gelatine block out on to a cool black glass 

 plate with the culture surface upwards, and trim the sides of 

 the gelatine block with a sharp scalpel dipped in methylated 

 spirit. 



(d) Select small superficial colonies and gently press a 

 clean cover-slip down over them. 



(e) Now carefully remove the cover- glass with the 

 impression of the colonies adhering to its under surface. 



(/) Gently warm the cover-glass and then pass it three 

 times through the flame. 



(g) Stain with Loffler's methylene-blue, or according to 

 Gram's method, and mount. 



Examine under a high power, and make a drawing of 

 the impression. 



