Letter from Howard Walter Florey to Joseph Song, University of Arkansas Medical Center, Little Rock Seem to be few differences between blood and lymphatic capillary vessels - refers to work by Casley-Smith - is not optimistic that Song will be able to detect differences between these vessels from the appearance of the endothelium - if Song can get something into the lumen of the lymphatic, might be possible to distinguish vessels by luminal content. 11 February 1963