10 



The Naturalist, 



Hence it follows, ttiat to completely extract a cochineal of indefinite 

 composition, the strength of the alcohol must be gradually increased 

 throughout. Acid makes the tincture lighter and more golden red. 

 Thus, by using acid alcohol (^-^ % hydrochloric acid, or 1 % acetic 

 acid), an overstaining can be easily corrected. On the other hand, 

 ammonia and other caustic alkalies, change the dye to a deep purple. 

 It is remarkable that the salts soluble in alcohol, give a blue-grey, 

 green- grey, or blue-black, precipitate with metals and alkaline earths. 

 For instance, if one treats some woven fabric, which has already been 

 dyed in cochineal and washed, with an alcoholic solution of iron or 

 chalk salts, a more or less dark blue dye is always obtained. As in 

 most cases, the salts existing in a living organism, are not altogether 

 removed in the process of preservation, but, in some cases even 

 increased ; it may often happen that, although the object may be put 

 in a red fluid, it will come out of it stained more or less blue, so that 

 it frequently happens that an object stained with cochineal, cannot be 

 distinguished from one treated with Eoematoxylin. The fact that the 

 blue colour results from the action of inorganic salts, and not from 

 the organic, is proved by the fact that powdered cochineal by being 

 extracted with an aqueous or alcoholic solution of chloride of calcium, 

 changes its colour, and the liquid has only a very slight red tinge. 

 In the same way, the cause of the deep colouring of the nucleus in 

 comparison with that of the remaining cell contents, must certainly 

 be referred to the properties of the organic matter. Naturally such 

 a precipitate in the nucleus cannot arise in the presence of acids ; so 

 that acid tissues, as well as those free from inorganic salts, will 

 always stain red. In a given case one cannot, therefore, say before- 

 hand what colour an object will be stained. Usually all Crustacea 

 with thick chitinous membranes are stained red. The remaining 

 animals are nearly all stained blue — so, that, for instance, the Vorti- 

 cellidcB which are found parasitic on the AmpJiipoda can be at once 

 recognised in a stained preparation, as foreign objects. The tissues of 

 one and the same animal often shew different colourings. For instance, 

 Kleinenberg has found that in the embryos of Limihricus the cell walls 

 stain deep red, while the cell contents become deep blue. In staining 

 glands it will be found that either they or their secretions frequently 

 become green, and on this account are easily recognisable. If it is 

 desired to have the plasma strongly stained, the object must not be 

 so thoroughly washed, but part of the colouring matter which is not 

 chemically bound up in the tissues, must be fixed by immersion in strong 

 alcohol. Slight remnants of acid appear to do less harm in this case 



