This study was carried out to determine the location and distribution of the defensive cells in normal lactating bovine mammary gland, whether there was any difference among five selected areas of the bovine udder. Another aim of this study was determination of antigenic stimulation on the defensive cell population.

As a material, tissue and milk samples taken from 10 noninfected lactating quarters and 10 subclinical mastitic ones were used.

Quantitative cytologic analyses demonstrated a marked and progressive increase in the concentration of the defensive cells from milk-secreting parenchymal tissues to the distal rosette region, near to the squamocolumnar junction in the normal lactating bovine mammary gland. The highest plasma cell concentrations were also found in the rosette area.

Antigenic stimulation caused a sharp increase in all defensive cell concentrations. The most striking increase occured in the epithelium and subepithelial connective tissues of Furstenberg's rosette. The increase in the plasma cell population was more striking compared with the other cell types.

Since the infectious agents generally reach at the parenchymal tissues through the streak canal, Furstenberg's rosette area which is highly populated with the defensive cells may play an important role in preventing the mammary tissues from invading mammary pathogens.