ZOOLOGICAL STATION IN NAPLES. 219 



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 

 from a few minutes to even days, according to the nature and size 

 of the object. With larger objects requiring considerable time, 

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

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

 proper depth of colour. Smafl 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 colour. This process requires, for larger objects, con- 

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

 alcohol slightly warm. 



The colour ultimately assumed by objects treated with cochi- 

 neal 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 go 

 per cent, or 1 00 per cent, alcohol have a light red colour, and stain 

 too diffusely to have any practical value. The weaker the alcohol 

 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 colour and 

 readiness of penetration ; 70 per cent, or 60 per cent, is recom- 

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

 favourable 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 



