82 METHODS OF CULTIVATION OF BACTERIA 



of water from which evaporation may take place. Tubes which 

 will require to be long in the incubator should have their plugs 

 covered either by india-rubber caps or by pieces of sheet rubber 

 tied over them. These caps should be previously sterilised in 

 1-1000 corrosive sublimate and then dried. Before they are 

 placed on the tubes the cotton-wool plug ought to be well singed 

 in a flame. " Cool " incubators are often used for incubating 

 gelatin at 21 to 22 C. An incubator of this kind fitted with a 

 low-temperature Hearson's regulator is in the market. 



Method of mounting Bacterial Cultures as Permanent 

 Museum Specimens. (Richard Muir). (a) Stab or stroke 

 cultures in nutrient gelatin or agar media. When the culture 

 shows typical characters, further growth is arrested by placing 

 tube in a formol vapour chamber, or by saturating the cotton- 

 wool plug with strong formalin. Then leave for a day or two. 

 Make up following : 



(1) Thymol Water (saturated in cold). . . 100 c.c. 



Glycerin 20 c.c. 



Acetate of Potasli . . . . . 5 grams. 



Coignet's (gold label) Gelatin ... 10 grams. 



Render the mixture acid to litmus with acetic acid ; clear with white 

 of egg and filter. 



Warm to about 40 C., and removing cotton-wool plug from 

 culture take a little of the preserving fluid in a pipette and 

 allow to run gently over surface of medium in tube. Place in 

 such a position that a thin layer of the preserving medium 

 remains completely covering the growth and the surface of 

 culture medium. The gelatin is now allowed to solidify. Add 

 three or four drops of strong formalin to the tube and fill up to 

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

 following fluid : 



(2) Thymol Water (saturated in cold) . . . 100 c.c. 

 Glycerin . . . . . . . 20 c.c. 



Acetate of Potash ...... 5 grams. 



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 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 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. 



