1. Effects of Embedding 2. Experiments with Modifications

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Abstract
Paraffin embedding was found to be satisfactory for brain stained by a modification of the Golgi dichromate-Ag method. Nitrocellulose embedding caused fading in a few specimens. Several modifications in which the tissue was impregnated with AgNO3 before treating it with K2Cr2O7 were investigated. The following one is recommended. Fix pieces of brain 5-6 mm. thick for 2 days in: AgNO3, 0.5%, 90 ml.; formalin, commercial unneutralized (37-40% gas), 10 ml.; pyridine, pure, 0.05-0.1 ml. Mix in the order given and test for pH with brom-cresol purple. A pH of 5.5-6 is about opt. and the amt. of pyridine added can be varied to adjust it. A slightly turbidity of the fixing fluid may be disregarded, but precipitation indicates too much alkalinity. Rinse the tissues with distilled water and place them in a mixture of K2Cr2O7, 2.5%, 100 ml. and osmic acid, 1%, 1 ml., for 3-5r days. Wash in water, dehydrate with alcohol and embed in soft paraffin for thick sectioning. Greater intensity of staining (but with an increase in precipitate) can be secured by rinsing the blocks after the dichromate treatment and resilvering in a 0.5% solution of AgNO3 for a day or 2, then washing, dehydrating and embedding. This modification of the Golgi method was worked out on brain of adult rat, guinea pig, cat and monkey. Results with fetal material were not good. All solns. used were aqueous, and staining was done at room temp.

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