[Light and electron microscopic investigations of the blood-milk barrier in lactating cow udders].

This paper reports a light and electron microscope (TEM) study of the blood-milk-barrier in the lacting mammary gland of the cow. The morphometric analysis of thick sections showed a significant difference between the posterior left quarter and the both right quarters of the udder. The distance between the endothelium of the capillary in the perialveolar connective tissue and the basal membrane of the secretory epithelium measures 2.33 microns. The thick sections used here have some important advantages over paraffin-embedded sections (cut at 5 microns), especially in connection with morphometric investigations. The electronmicroscope observations revealed the following remarkable structures in the blood-milk-barrier: 1. The endothelium of the capillaries in perialveolar connective tissue contains many pinocytotic vesicles and possesses pseudopodic structures. 2. The myoepithelial cells do not appear continuously and are therefore only indirectly related to the barrier. 3. The basal system contains special folds of epithelial cells.