88 METHODS OF CULTIVATION OF BACTERIA 



which will require to be long in the incubator, the plugs should 

 be pushed a little way into the tube and a few drops of 

 melted paraffin dropped on the top of the wool, or the plugs 

 should be covered either by indiarubber 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 tube 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 the 

 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 the following : 



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

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



Acetate of potash ...... 5 grms. 



Coignet's (gold label) gelatin .... 10 grms. 



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

 of egg and filter. 



Warm to about 40 C., and removing cotton-w T ool 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 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 to near the top of tube; allow to solidify. Cover 

 paraffin with layer of alcoholic orange shellac cement; allow 



