In presenting his valuable technique for the histochemical demonstration of acid phosphatase, Gomori ( '41) remarked on the variable character of the pictures sometimes obtained. This variability is not a handicap in tissues which have a high phosphatase content, but I have found that it virtually precludes the achievement of consistent results in early embryonic tissues, in which the enzyme concentration is generally low.
A search for a suitable activator for the acid phosphatase of the chick embryo led to the discovery that manganous sulfate, added to the lead nitrate-sodium glycerophosphate incubating solution, has a marked and peculiar effect. Ordinarily the deposits that arc visualized when the lead phosphate formed during the course of incubation is treated with sulfide range from pale golden-brown to black, and appear to be spread evenly through the cells in which the enzyme acts. After incubation with manganese however, even tissues which are very poor in acid phosphatase show deposits that are always intensely black, and are laid down in the form of fine discrete granules. These granules, even when few in number, appear with gratifying consistency in differ- ΒΆ Aided by a grant from the Rockefeller Foundation t o Washington I'niversity.