78 THE AMERICAN MONTHLY, [March, 



the thin cover. We then replace the picro-carmine by a preserva- 

 tive Hquid, with precautions to be referred to hereafter. Tissues 

 fixed by osmic acid or by the bichromates are stained by picro-car- 

 mine with great difficuhy .... Such sections are placed for 24 

 hours in a corked tube filled with a mixture of equal parts of picro- 

 carmine and water. They are then washed, and mounted as 

 described for sections treated with alcohol. This does not give 

 the fine results obtained by the preceding method. The wash- 

 ings needed to remove the picric acid destroy those shades of 

 color obtained by the action of picro-carmine .... 



Alum carmine. — . . . . Ammonia alum, i to 5 grms. ; car- 

 mine, 4 grms. ; distilled water, 100 grms. Boil for 30 minutes, 

 taking care to maintain the original volume by adding water. 

 Filter and preserve by a crystal of thymol. It is a nuclear stain 

 of the first order; it colors admirably the nuclei of tissues fixed 

 by osmic acid, which makes it valuable in many cases where 

 picro-carmine is worthless. And, further, the color is well 

 preserved in glycerin. Place the sections for a few hours in a 

 vessel containing one c. c. of alum carmine, and wash until the 

 excess of color has been removed. 



This stain is exceedingly penetrating, so that tissues may be 

 colored '• in mass." After washing, which follows the action 

 of the fixative, place the specimen in a test-tube containing 2 or 

 3 c. c. of alum carmine. After a variable time (one or two 

 days) transfer to water, which should be renewed as long as it is 

 tinged with carmine. The tissue is then passed through alcohol 

 and imbedding materials. . . . 



Haematoxylin. — . . . . With a little attention it is here 

 possible to get good coloring after all fixing reagents, but to 

 obtain perfect nuclear selection the htematoxylin should be 

 applied to pieces fixed by the bichromates. The best way to 

 use it is to put the sections in a vessel with a few drops of the 

 stain. If the tissue has not been long in the bichromate, it will 

 stain in from 15 to 20 minutes ; with other reagents, one or two 

 hours are needed. When stained, wash in water and mount 

 in balsam ; gh^cerin destroys the color. Beautiful preparations 

 may be had by combining hjematoxylin and eosine. 



Aniline colors. — . . . . Of these, procure methyl green, 

 eosine, quinolein blue, safranine, gentian violet, and methyl 

 blue. The best way to use them is to make saturated solutions 

 in absolute alcohol, and keep in well-stoppered bottles. They 

 should be filtered when needed, and diluted with an equal 

 volume of distilled water. . . . Eosine is habitually used as a 

 complement to Ranvier's htematoxylin, by placing the section 

 stained by hajmatoxylin on the slide, washing it well, and 

 coloring with eosine in alcohol or in water. . . . 



Impregnations. — This name is given to the coloring pro- 

 duced by the formation within the elements of metallic deposits 

 in a state of very fine subdivision. Nitrate of silver and chloride 

 of gold are always used for this purpose. 



