The lymphatic tissue of the rabbit contains a labile peptidase as measured by the hydrolysis of alanylglycine. Some characteristics of the enzyme were determined. This enzyme increases in amount when the numbers of macrophages in the tissue are increased and it is also present in the extracellular fluid in high concentration. The extracellular fluid value for this activity is calculated to be about 8 times the value for serum. Based on a correlation between the types of cells present and the amount of peptidase found in the tissue the following relative activities are assigned to the tissue components per unit volume: lymphocytes 1.0, tissue fluid 11.0, serum 1.4, phagocytes (macrophages) 30.0, reticular cells 12.0. The amount of chloride space varied from 35 to 55 per cent.
The relative amounts of acid phosphatase per unit volume in the same elements were calculated to be: lymphocytes 1.0, tissue fluid 0, phagocytes 20.0, and reticular cells 4.0.
Analysis of the distribution of peptidase was facilitated by simultaneous determination of acid phosphatase whose primary localization in one cell type was known.
The over-all contribution of lymphocytes to the labile peptidase content of lymphatic tissue is relatively minor and was not found to exceed 5 per cent of the average value for the entire nodular tissue. In the absence of large numbers of macrophages the intercellular fluid of the nodule accounts for half or more of the peptidase content of the nodules.