1 882.] in the Zoological Station in Naples. 775 



it is important to use a large quantity of the fluid, otherwise the 

 amount of coloring stuff in solution might not suffice to give the 

 proper depth of color. Small and delicate objects, on the other 

 hand, may be most successfully treated with a solution which has 

 been diluted with 70 per cent, alcohol, or one which has been 

 weakened by previous use. It is always necessary to free the tis- 

 sues, after staining, from the surplus dye; and this may be done 

 by washing in 70 per cent, alcohol, which must be changed until 

 it shows no color. This process requires, for larger objects, con- 

 siderable time and alcohol, but may be hastened by using the 

 alcohol slightly warm. 



The color ultimately assumed by objects treated with cochineal 

 tincture varies much, and depends partly on the reaction of the 

 tissues themselves, partly on the presence or absence of certain 

 salts. It is certainly one of the best recommendations of this 

 staining agent that, varying with the nature of the object and its 

 mode of treatment both before and after staining, it gives such an 

 extraordinary diversity of results. On account of the great 

 variety of substances contained in the dried dye-stuff, it is evident 

 that the composition of the tincture must vary according to the 

 strength of the alcohol employed as a solvent. Solutions in 90 

 per. cent, or 100 per cent, alcohol have a light red color, and stain 

 too diffusely to have any practical value. The weaker the alco- 

 hol the stronger the tincture, and the stronger the alcohol the more 

 easily it penetrates objects ; the grade of alcohol may therefore 

 be selected with reference to two points, depth of color and readi- 

 ness of penetration ; 70 per cent, or 60 per cent, is recommended 

 by Dr. Mayer as combining both these qualities in a very favor- 

 able degree. It is important to remember that whatever be the 

 strength of the solution, a precipitate will always be produced if 

 an alcohol of a different grade, whether higher or lower, be mixed 

 With it. It is evident then that a tincture of any given strength 

 contains substances that are insoluble in any other grade of alco- 

 hol, and this explains why superfluous coloring matter can only 

 be removed from objects by the aid of alcohol of precisely the 

 same degree as that of the tincture. 



. Over staining, which seldom occurs, may be easily corrected 

 by the aid of acid alcohol (^ per cent, hydrochloric acid, or 1 per 

 cent, acetic acid). Acid makes the tincture lighter, more yellow- 

 ish-re J, while the addition of. ammonia and other caustic alkalies 



