84 BACTERIA IN THE SPUTA 



the slide a drop of aniline water, taken from the relative bottle, 

 and soon after add a colouring solution. For, by placing the 

 solution first and the aniline water afterwards, we obtain a greater 

 precipitation of coloured granules in the preparation. 



It is necessary that the particle of sputum should be well 

 immersed in the colouring mixture, so as to have it well coloured 

 on its under as well as its upper surface ; because, if the particle 

 is placed on the slide before the solution, the part adhering to the 

 glass cannot be coloured. The particle of the sputum should not 

 be larger than i/4th to i/3rd of a grain of millet ; otherwise, 

 when pressed between the two slips, it will press out from under 

 the cover-glass, and consequently the best specimens, which are on 

 the edges, will be lost, or the preparation will prove too thick for 

 investigating the most delicate parts. 



The particle of sputum, taken with a bent needle, should be 

 immediately put into the colouring mixture, pressed down for a 

 short time with the needle, then left for two hours under a watch- 

 glass ; a drop of distilled water may be added to it, if a weaker 

 colouring be desired ; or, in hot weather, to prevent hardening or 

 evaporation. 



After the required time has passed, take the sputum with a 

 perfectly clean needle, put it in a watch-glass containing distilled 

 water, and, by gentle agitation, it will be freed from the granular 

 deposits. Meanwhile the slide must be well cleansed. Then put 

 upon it a drop of distilled water, in which the particle is to be 

 again immersed. By using glycerine we cannot obtain the proper 

 thinness of the preparation, and many features would appear to be 

 altered and colourless. Glycerine can ultimately be substituted 

 by capillarity to preserve the preparation, the upper surface of the 

 cover-glass, made greasy by the immersion, being washed first with 

 benzoin and then with water. 



In the preceding Memoir, we recommended the spreading and 

 thinning of the particle of the sputum with needles ; but for our 

 present investigation it would not be advisable to do so. It was, 

 perhaps, owing to this that we then lost some details, especially 

 with regard to the fructifications of Leptothrix. In fact, spreading 

 with needles must destroy the relations of continuity and contiguity 

 necessary to preserve intact the said fructifications. 



