774 Methods of Microscopical Research [October, 



centrated solution of crystallized hematoxylin in absolute alco- 

 hol as suffice to give the required depth of color. 1 



If the color appears too strong-, the fluid may be diluted with 

 solution No. I. 



Before immersing objects in this fluid, great care should be 

 taken to free them from the least trace of acid by frequently 

 changing the alcohol. If this is not done thoroughly, the acid 

 left in the preparation will sooner or later cause the color to fade; 

 and such results have led to the erroneous conclusion that haema- 

 toxylin will not give durable preparations. Dr. Mayer has found 

 that the fading is entirely due to the presence of acid, and that 

 with proper precautions the staining is permanent. 



Small objects are best stained in a weak solution, which colors 

 more slowly but with greater clearness than stronger solutions. 

 After staining, Kleinenberg transfers objects to 90 per cent, alco- 

 hol. In case of over staining, the color may be partly removed 

 by adding a little oxalic acid or hydrochloric acid (}4 per cent, or 

 less) to the alcohol containing the objects. The acidulated alco- 

 hol is allowed to work until the color is slightly reddened. On 

 transferring to pure alcohol the color passes again into a perma- 



2. Mayer s cochineal tincture. — 1 gramme powdered cochineal 

 soaked in 8-10 can. 70 per cent, alcohol for several days, then 



The clear deep red fluid thus prepared may, like haematoxylin, 

 be used in all cases where it is desirable to stain with an alcoholic 

 solution, and will be found particularly useful for objects that are 

 not easily penetrated by the ordinary aqueous solutions of car- 

 mine, such as the Arthropods. 



It is necessary, before immersing larger objects in this fluid, to 

 leave them a short time in 70 per cent, alcohol, otherwise there 

 may be a precipitate. The time required for staining, will vary 



of the object. With larger objects requiring considerable time, 



