1. Tissue sections eight microns thick were exposed to various experimental conditions used in histochemistry, and the effect upon the activities of esterase, the phosphatases, leucine aminopeptidase, ß-glucuronidase, and arylsulfatase was determined colorimetrically.

2. Significant differences were found in the amounts of the lyo and desmo fractions of these enzymes. The desmo components were found to be for esterase, alkaline phosphatase, leucine aminopeptidase, acid phosphatase, ß-glucuronidase, and arylsulfatase, ⅓, 2/3, 2/3, ½, ⅛, and ⅛ of the total enzymatic activity respectively.

3. Variations in the time and in the temperature at which diffusion was studied and of the pH and salt concentration of the solution into which the sections were placed, resulted in differences in the amount of enzymatic activity which remained in the tissue section. Some enzyme loss by diffusion was noted even after fixation of the tissue section.

4. The significance of the findings with respect to some of the concepts of localization of enzymes in tissue sections was discussed.

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