b. =Orange G.= Used in a 1 per cent water solution. Requires longer time for staining than eosin. c. =Acid Fuchsin.= A saturated water solution is kept in stock and diluted as needed. Must be used in weaker solutions than eosin, as it more quickly overstains, and cannot be washed out so well. d. =Picric Acid.= Keep in stock either a saturated water or saturated alcoholic solution, and dilute as needed. As it washes out more readily than eosin, the staining solution should be stronger than for the latter, and the sections somewhat over-stained to allow for some loss of stain. Picric acid gives a brownish tint to nuclei stained with hæmatoxylin or carmine, and will take out the stains completely, if allowed to act too long. e. =Ammonia Carmine.= One grm. of carmine is dissolved, without heating, in 50 cc. of distilled water and 5 cc. of strong ammonia water. The fluid is then exposed in an open dish until the odor of ammonia is lost; it is then filtered. When ready for use dilute by filtering 1-2 drops into 20 cc. of distilled water. III. COMBINED NUCLEAR AND DIFFUSE STAINS. The diffuse or plasma stains may be combined with the nuclear in one staining solution, or used in succession. The latter method gives better results. The nuclei are stained first, the diffuse stain being used after the washing-out following the use of the nuclear stain, except in the methylene-blue and eosin method in which to obtain the best results it is necessary to stain with the eosin first. Nuclear hæmatoxylin may also be followed by a combination of plasma stains, as in the Van Gieson’s mixture of picric acid and acid fuchsin, Delépine’s mixture of rubin and orange, White’s erythrosin and picric acid mixture, etc. In these mixtures the different affinities of the plasma-stains give rise to differential or selective staining effects. a. =Haematoxylin and Eosin.= 1. Stain in any one of the hæmatoxylins. 2. Wash thoroughly. 3. Stain in dilute water or alcoholic eosin until section is bright rose-red. 4. Differentiate eosin-staining, as desired, by rapid or slow washing in water. 5. Dehydrate quickly in 80 and 95 per cent alcohols. 6. Clear quickly in carbol-xylol. (If carbol-xylol takes out eosin too rapidly add some of the dry eosin stain to it. Hæmatoxylin-stained sections can be placed in such eosin-carbol-xylol and will take up the eosin beautifully.) 7. Mount in balsam. Hæmatoxylin and eosin can also be combined in one stain, but the results are not as good as those obtained by successive staining. b. =Haematoxylin and Picric Acid.= 1. Stain with Weigert’s iron-hæmatoxylin, or overstain with any other hæmatoxylin. 2. Wash thoroughly. 3. Stain in saturated water solution of picric acid, diluted one-half, until sections are a bright yellow. If left too long in the stain, the hæmatoxylin will become brown or may be wholly lost.