STAINING AND EXAMINATION OF MICRO-ORGANISMS 4.9 



(3) Placed in alcohol for half a minute. 



(4) For ten seconds in 3 per cent, alcoholic hydrochloric acid. 



(5) At the end of ten seconds it is at once immersed in fresh pure 

 alcohol for several minutes. 



(6) After being transferred once or several times to fresh alcohol in 

 order to remove the maximum amount of colour it is placed in xylene. 



(7) In xylene the section may remain for any length of time, as it 

 undergoes no change in it. After being saturated with xylene for not less 

 than half a minute, it may be placed on the microscopic slide. 



(8) After soaking up the excess of xylene a drop of xylene balsam is 

 placed 011 it and the cover-glass superposed. 



If it is desired to colour the nuclei of the tissue as 

 well as the bacteria, and so stain the preparation in two 

 colours, it is advisable to stain the nuclei before the 

 bacteria ; this can be done as follows : The freshly 

 prepared unstained sections are taken out of the alco- 

 hol, and instead of proceeding as above they are placed 

 for several minutes in water, and then in a picrocar- 

 mine solution (picrocarmine does not stain bacteria) for 

 from one to two minutes. (The picrocarmine solution 

 is thus prepared : To 50 parts of distilled water add 

 1 of carmine and 1 of ammonia ; to this add a solution 

 of concentrated aqueous picric acid until no more 

 carmine is precipitated.) The section is washed four 

 or five times in water and then placed in alcohol. 

 The cell-nuclei are now beautifully stained with car- 

 mine, and the section may remain unharmed for a con- 

 venient time in the alcohol, after which it can be 

 stained according to the Gram-Giinther method, pro- 

 ceeding exactly as if it were a colourless preparation, 

 the cell-nuclei retaining their tint without the least 

 alteration during the process. 



It is very important to note that fuchsine, metliy- 

 lerie blue, and Bismarck brown cannot be used for 

 Gram's method, but only the so-called pararosaniline 



specimens by adopting this precaution. Centralblatt fiir Baliteriologie, 

 vol. xi. p. 231, 1892. 



E 



