THE ORDINARY STAINING SOLUTIONS. 127 



the colony from which the preparation was made. They 

 are made by gently covering the colony with a thin, 

 clean cover-slip, lightly pressing upon it, and, without 

 moving the slip laterally, lifting it up by one of its 

 edges. The organisms adhere to the slip in the same 

 relation to one another that they had in the colony. 

 The subsequent steps of drying, fixing, staining, and 

 mounting are the same as those just given for the 

 ordinary cover-slip preparations. 



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 together, others will grow in parallel bundles, 

 while others, again, will be seen as long twisted threads. 



THE ORDINARY STAINING SOLUTIONS. The solu- 

 tions commonly employed in staining cover-slip prepara- 

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

 aniline dyes fuchsiu, gentian-violet, and methylene- 

 blue. These solutions may be prepared either by directly 

 dissolving the dyes in substance in water until the proper 

 degree of concentration has been reached, or by prepar- 

 ing them from concentrated watery or alcoholic solutions 

 of the dyes which may be kept on hand as stock. The 

 latter method is that 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 solutions 

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

 solutions are best prepared by pouring into clean bottles 

 enough of the dyes in substance to fill them to about 

 one-fourth their capacity. The bottle should then be 

 filled with alcohol or with water, tightly corked, well 

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



