132 A MANUAL OF BACTERIOLOGY 



(c) McCrorie's method 1 (modified by Morton 2 ). Prepare the 

 following solutions : 



A. Tannic acid ...... 1 grin. 



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, and then placed in the following solution for twenty-four 

 to forty-eight hours : 



Formalin ...... 6 parts 



Sodium chloride ..... 1 part 



Sodium sulphate ..... 2 parts 



Magnesium sulphate . . . . .100 parts 



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



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



