(1) The results of comparative staining of hair cortex, posterior pituitary, and several tissue lipids, with leukofuchsin, aldehyde-fuchsin, and toluidine blue, after a variety of pretreatments, are presented. (2) The results confirm those of Lillie and Bangle, that induced Schiff-positivity of hair cortex is not due to oxidation products of cystine, while the metachromatic basophilia induced in hair cortex by appropriate reagents is so explained. However, whether the reactive group responsible for the Schiff-positivity is a part of keratin or of some other molecular entity has not been established. (3) Preliminary results with four additional reagents capable of producing histochemically demonstrable products from ethylenic groups are presented. Selenium dioxide appears to have little promise for this purpose, and osmic acid potassium chlorate appears to oxidize both lipids and cystine. Iodoform peracetic acid has provided evidence of the occurrence of unsaturated entities, perhaps lipids, in hair cortex. Phosphorus pentachloride may have value as a reagent for demonstration of certain lipids by means of induced basophilia, but the mechansim of phosphate radical binding may well be esterification rather than substitution into ethylenic groups. (4) Aldehyde-fuchsin appears to have particular affinity for certain reactive groups, of unknown nature but possibly neither carbonyl nor acid radicals, which are produced in sections by treatment with sulfuric acid permanganate. (5) Phosphorus pentachloride, like phosphoryl chloride, leads to leukofuchsin-positivity of certain tissue entities. No evidence that this reaction is not due to carbonyl groups was obtained, but phosphorylating agents are of interest with regard to the chemical nature of reactive groups responsible for certain Schiff reactions.