MOUNTING OF BACTEEIAL CULTUKES 87 



within a quarter of an inch of the top of the tube with the 

 following fluid : — 



(2) Thymol water (saturated in cold) ... 100 o.c. 

 Glycerin ... . . 20 c.c. 

 Acetate of potash 5 grms. 



Cover top of tube with a small piece of paper so as to keep out 

 dust, allow to stand for a day or two so that small air-bells may 

 rise to the surface. 



To seal tube, pour melted paraffin gently on to the surface 

 of fluid up to near the top of tube ; allow to solidify. Cover 

 paraffin with layer of alcoholic orange shellac cement; allow 

 this to set, and repeat until the cement becomes level with top 

 of test-tube. When the cement is set, a few drops of black 

 lacquer are put on, and a circular cover-glass of about the 

 same diameter as the mouth of tube is placed so as completely 

 to seal it. 



, (b) The following method is useful for preserving plate cultures : 

 Instead of making the cultures in Petri's capsules, use ordinary 

 watch-glasses. The watch-glass is sterilised in a Petri's capsule, 

 and the inoculated medium is poured out into the watch-glass, 

 allowed to solidify in the usual way, and left in the Petri's 

 capsule until the colonies of growth have developed. The 

 watch-glass is now removed from capsule, and a layer of the pre- 

 serving gelatin medium (1) (p. 86), to which have been added a few 

 drops of strong formalin, is allowed to spread over the surface 

 of the culture medium. When the layer is solidified the watch- 

 glass is filled up with the same, and a clean square or oblong 

 piece of glass (which of course should be of slightly larger 

 diameter than the watch-glass) is now carefully placed over 

 watch-glass, care being taken that no air-bells are formed. The 

 edge of watch-glass should be closely applied to the glass cover, 

 and left in position until the gelatin has solidified. The super- 

 fluous gelatin is now removed, and the glasses sealed first with 

 the orange shellac cement, then with black lacquer. It is now 

 finished off by using a circular mask of suitable size. 



The various kinds of solid media used in the cultivation of 

 bacteria, such as blood serum, potato, bread paste, etc., can be 

 treated* in the same manner with excellent results. 



General Laboratory Rules. — On the working bench of every 

 bacteriologist there should be - a large dish of 1-1000 solution of 

 mercuric chloride in water. Into this all tubes, vessels, plates, 

 hanging-drop cultures, etc., which have contained bacteria and 

 with which he has finished, ought to be at once plunged (in the 



