The application of histochemical methods in the study of the skin in leprosy; demonstration of bacillus-containing capillaries and axons by treatment for phosphatases.

Histochemical methods have been devised Lo demonstrate certain metabolic activities of cells. By these techniques certain structures in a particular tissue are made to stand out in contrast to the other constituents. We have applied the methods for demonstrating alkaline and acid phosphatase activity to the study of the skin in leprosy. Pearse (5) has pointed out that these methods depend on incubating the tissue with a substrate which contains an organic phosphate (sodiumB-glycerophosphate being usually used). Phosphate will be liberated at the site of phosphatase activity. If the pH of the solution is 9.0 or above, alkaline phosphatase is responsible for the phosphate liberated. If the pH of the solution is between 5.0 and 6.0, acid phosphatase effects the liberation of phosphate. To fix the phosphate where it is liberated, a calcium salt is added to the substrate used for alkaline phosphatase activity. which precipitates the phosphate as calcium phosphate. That product is t.hen replaced by brownish-black cobalt sulphide by first placing the tissue in cobalt nitrate and then in a solution of yellow ammonium sulphide. Structures which contain alkaline phosphatase can be recognized in the tissues by their brownish-black color. In the acid solution, however, calcium phosphate will not precipitate as it is soluble in those conditions. Lead nitrate therefore replaces the calcium salt in the incubation mixture, and lead phosphate is precipitated at the site of acid phosphatase activity. The lead phosphate is then converted into black lead sulphide by treatment with yellow ammonium sulphide.