ORDINARY STAININQ-SOLUTIOm. 163 



steps of drying, fixing, staining, and mounting are the 

 same as tliose just given for ordinary cover-slip prep- 

 arations. 



By this method constancies in the arrangement and 

 grouping of the individuals in a colony can often be 

 made out. Some will always appear irregularly massed, 

 others show growth in parallel bundles, while others, 

 again, will be seen as long, twisted threads. 



Note. — From a colony of bacillus subtilis make a 

 cover-slip preparation in the ordinary way ; now make 

 an impression cover-slip preparation of another colony 

 of the same organism. Compare the results. 



Oedinaey Staining-solutions. — The solutions 

 commonly employed in staining cover-slip preparations 

 are, as has been stated, watery solutions of the basic 

 aniline dyes — fuchsin, gentian-violet, and methylene- 

 blue. These solutions may be made either by directly 

 dissolving the dyes in substance in water until the 

 proper degree of concentration has been reached, or by 

 using concentrated watery or alcoholic solutions of the 

 dyes which may be kept on hand as stock. The latter 

 method is the one commonly practised. 



The solutions of the colors which are in constant use 

 in staining are prepared as follows : 



Prepare as stock, saturated alcoholic or watery solu- 

 tions of fuchsin, gentian-violet, and methylene-blue. 

 These solutions are best made by pouring into clean 

 bottles enough of the dyes in substance to fill them to 

 about one-fourth of their capacity. Each bottle should 

 then be filled with alcohol or with water, tightly corked, 

 well shaken, and allowed to stand for twenty-four hours. 



