CASTING METHODS OF SCANNING ELECTRON-MICROSCOPY APPLIED TO HEMAL LYMPH-NODES IN RATS

Hemal lymph nodes of the para-aortic group in rats were examined by sc anning electron microscopy (SEM) using the corrosion cast technique. T he vasoarchitecture of hemal lymph nodes was described in cast specime ns filled from the abdominal aorta. A dense system of capillaries arra nged in the mode of a meshwork could by represented in the nodal corte x. The postcapillary venule (PCV) with wide vascular lumina provided t he prevailing vessel type of the deep cortex. Sphincter-like narrowing s of the capillary lumen appeared at the sites where capillaries merge d with the PCV. These vascular segments were interpreted as structures controlling the hemodynamics of the joining PCV thereby providing app ropriate conditions for homing lymphocytes. No evidence was obtained f rom the casts for an open circulation in hemal lymph nodes. The intran odal lymphatic pathways were studied in specimens interstitially injec ted with resin. The fine lymphoid tissue spaces were characterized by special cast patterns reflecting the structural differentiation of cer tain nodal compartments. Afferent lymphatics could be clearly identifi ed in casts with a retrograde filling from the subcapsular sinus. Very spacious intermediary sinuses and wide-meshed medullary sinuses could be represented in those casts as well, thus allowing ample space for the encounter of large macrophages with red blood cells.