876 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Usually, all Crustacea with thick chitinous parts are stained red, 

 and most other animals blue ; so that, for instance, the Vorticellidae, 

 which are parasitic on the Amphipoda, can be at once recognized as 

 foreign bodies. Very often the different tissues of one and the same 

 object present unlike colours. In the embryos of Lumbricus, Kleinen- 

 berg found the walls of the blood-vessels red, their contents dark- 

 blue. Glandular tissues, or their contents, are frequently stained 

 grey-green, and on this account are easily recognizable. 



Objects when previously treated with chromic or picric solutions, 

 or with alcohol, usually stain without difficulty ; but osmic acid 

 preparations should be bleached before staining. Cochineal does 

 not colour so intensely as hematoxylin, and hence the latter often 

 gives more satisfactory results in the case of large objects stained 

 in toto. 



As before pointed out, alcohol causes the salts contained in sea- 

 water to be precipitated, thus forming a crust on the exterior of the 

 animal, which interferes with the staining process. It is therefore 

 necessary to treat marine animals that have been preserved in strong 

 alcohol, with acid alcohol (1-10 parts hydrochloric acid to 1000 parts 

 70 per cent, alcohol), and then carefully wash in pure 70 per cent, 

 alcohol before staining with cochineal. 



3. Carmine and Picrocarmine. — Aqueous solutions of staining 

 media are generally only used when alcoholic cannot be employed. 

 The interpretation of the results obtained by carmine staining is not 

 always satisfactory. For instance, in his work on the nervous system 

 of Aquilla, Bellona describes the peculiar crescent-like structures in 

 the ganglion cells. Dr. Mayer is of opinion that these are entirely 

 artificial productions, and owe their origin to the carmine (Beale's) 

 solution in which they were stained, for with careful preparation 

 they do not appear. Picrocarmine is more certain in its results, 

 and in some cases will give better specimens than can be obtained 

 by any other medium. In commerce it often contains too much 

 picric acid, and it is better to prepare it oneself in the following 

 manner : — 



To a mixture of powdered carmine (2 g.) with water (25 ccm.), 

 while heating over a water-bath, add sufficient ammonia to dissolve 

 the carmine. The solution may then be left open for a few weeks 

 (Mayer) in order that the ammonia may evaporate ; or the evaporation 

 may be accelerated by heating (Hoyer). So long as any ammonia 

 remains, large bubbles will form while boiling, but as soon as the free 

 ammonia has been expelled, the bubbles will be small and the colour 

 of the fluid begin to be a little lighter. It is then allowed to cool, and 

 filtered. To the filtered solution is added a concentrated aqueous 

 solution of picric acid (about four volumes of the acid to one of the 

 carmine solution). The addition of the acid should cease before a 

 precipitate begins to form. 



In order to protect this fluid against changes attributed to bacteria 

 by Hoyer,* Dr. Mayer places a small crystal of thymol in the con- 



* Hoyer, « Beitr. z. histolog. Technik.," Biol. Centralbl., ii. (1882) pp. 17-19. 



