Abstract
We report on the observation of a thread-like structure, which is a semi-transparent elastic bundle of tubules, inside the blood vessels of rats and rabbits. We contrived a method using an intravenous injection of a 10 % dextrose solution at the vena femoralis to cause blood to coagulate around an intra-blood-vessel duct (IBVD) so that it became thick and strong. The tubular substructure of the IBVD was observed by using a differential interference contrast image and by using an electrical separation technique. The functions of the IBVD are not known at the present time. We might speculate that the IBVD is a Bo