48 MICRO-ORGANISMS IN WATER 



clove oil, by means of which some more colour is 

 extracted. Grain found, however, that all micro- 

 organisms are not similarly affected by this method of 

 treatment, for whilst some retain, others lose the stain 

 when submitted to the process ; the latter may there- 

 fore be made use of not merely for distinguishing the 

 micro-organisms from other materials with which they 

 occur, but also as a valuable means of differentiation 

 between various micro-organisms themselves. The 

 method thus acquires a wider importance than that 

 which attaches to the purpose for which it was origin- 

 ally intended. 



Gram-G'iinther method. Giinther has modified 

 Gram's original method by giving the preparation an 

 additional washing with a 3 per cent, alcoholic hydro- 

 chloric acid after the alcoholic washing employed by 

 Gram, and also by substituting xylene for clove oil. 



The following is the description of this modified 

 method given by Giinther himself : l 



(1) The section is taken out of the alcohol and immersed in a freshly 

 filtered solution of Ehrlich's aniline water gentian violet or methyl 

 violet for from one to two minutes. 3 The solution must have been pre- 

 pared at least twenty-four hours previously. 



(2) The section is removed with a needle, the surplus colour taken off 

 with blotting-paper and placed in the solution of iodine and potassium 

 iodide 3 for two minutes. The section should lie well spread out on the 

 bottom of the dish. 



1 Einfilhrung in das Studium der Baltteriologie mit besonderer 

 BerilcTtsiclitigung der mikroskopisclien Technik. Leipzig, 1893. P. 102. 

 3rd edition. 



2 With tubercle and leprous sections the time is longer ; in the case 

 of the former from twelve to twenty-four hours are required, whilst in the 

 latter half an hour is sufficient. 



3 Botkin advises, before treating the preparation with the iodine and 

 potassium iodide solution, to wash it well with pure aniline water to re- 

 move the surplus colour, and then proceed as above. He states that the 

 colour is thus more easily removed, and the preparation can remain for 

 a much longer time in the iodine and potassium iodide without suffer- 

 ing any damage that in fact he has obtained cleaner and better stained 



