116 A MANUAL OF BACTERIOLOGY 



preserved in separate bottles. For use equal quantities are mixed 

 together. The specimens are flooded with the mixture and held 

 over the flame until it nearly boils ; they are then laid aside, with 

 the hot stain on them, for one minute, and are finally washed in 

 water. After washing, the preparations are flooded with anilin 

 gentian violet for one second, washed in water, dried and mounted, 

 (c) McCrories method x (modified by Morton 2 ). Prepare the 

 following solutions : 



A. Tannic acid ....... 1 grm. 



Potash alum ...... 1 grm. 



Distilled water . . 40 c.c. 



B. " Night " blue . ... 0-5 grm. 

 Absolute alcohol . . . . . .20 c.c. 



Mix and filter. 



The prepared slides are stained with this solution (which should 

 always be filtered before use) for two minutes, the solution being 

 changed two or three times, washed gently in running water, and 

 then counter-stained in anilin gentian violet for one to two minutes, 

 washed, dried, and mounted. 



Preservation of Cultures 



Gelatin and agar cultures may be satisfactorily preserved by 

 submitting them to the action of formaldehyde vapour for some 

 hours by soaking the wool plug of the culture tube in formalin and 

 plugging the tube with it. The tube may then be sealed with 

 gutta-percha tissue, sealing-wax, or paraffin wax, or best of all in 

 the blowpipe flame. Plate cultivations may also be exposed to the 

 vapour and the lid of the dish afterwards cemented on, or the 

 cultures may be made in the flat bottles ("Soyka's bottles") 

 devised for the purpose, and after development treated like tube 

 cultures. 



Preservation of Pathological Specimens 



These may be preserved in the ordinary way in spirit, but a much 

 better method, by which the natural colour of the specimen is 

 retained, is the following. The specimens are first washed in water, 



1 Brit. Med. Journ., 1897, vol. i, p. 971. 



2 Trans. Jenner Inst. Prev. Med., vol. ii, p. 242. 



