86 METHODS OF CULTIVATION OF BACTERIA 



22° C. An incubator of this kind fitted with a low-tempera- 

 ture Hearson's regulator is in the market. 



Fig. 35. — Hearson's incubator for use at 37° C. 



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-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 



