142 ENTOMOLOGICAL NEWS. | May. '19 



The Staining of Coccids (Homop.).* 



By J. HOWARD GAGE. 



Students of the Coccidae have long desired a stain that 

 would permanently color the chitinous exoskeleton and at 

 the same time give enough contrast to make the more minute 

 details of structure plainly visihle under the microscope. Un- 

 til the present time such a stain has not been found. In most 

 cases in specimens that have been stained the color disinte- 

 grates with age, leaving them muddy, and in fact, in a much 

 worse condition for study than they would have been had no 

 stain been used. 



In my work with the Coccidae several of the more common 

 stains were tried, one by one they were discarded until only 

 saurefuchsin remained. This substance gave on the whole 

 the best results, but even in specimens colored with this stain 

 the color faded after a time. Saurefuchsin is, as the name 

 implies, an acid stain having enough acid combined with the 

 coloring properties of the substance to produce acidity, pro- 

 viding the specimen treated is neutral or acid. It is evident, 

 then, that the presence of an alkali even in minute quantities 

 will impair the working of the stain, for such an alkali would 

 neutralize the acid of the stain and cause it to break down. 

 To remove all traces of the potassium hydroxide ordinarily 

 used in cleaning specimens requires more than the customary 

 three or four baths of distilled water ; in fact one can never, 

 according to the theory of limits, remove all of the alkali 

 simply by washing, even though one might reduce it to a 

 negligible quantity. In order to prevent any alkali being 

 present, a ten per cent, solution of hydrochloric acid was add- 

 ed to the staining solution. This excess of acid neutralized 

 the small amount of potassium hydroxide that remained, pre- 

 cipitating it as a potassium salt, leaving an excess of hydro- 

 chloric acid in the staining solution and the specimen. 



HC1 (in excess) + KOH = = KC1 + HOH + HC1. 



The precipitated potassium chloride is very highly soluble in 

 water, but since all of the water is removed during the de- 

 hydration of the specimen there remains nothing except a few 

 crystals of potassium chloride and hydrochloric acid in ex- 

 cess. As there is an excess of acid in the specimen, it is clear 

 that if it be mounted and sealed in with acid balsam it will 



^Contributions from the Entomological Laboratories of the Univer- 

 sity of Illinois. No. 59. 



