The dimensions and numbers of small vesicles in blood capillary endothelium in the hind legs of dogs, and their relation to vascular permeability

The dimensions and numbers of vesicles were determined in the blood capillary endothelium of the gastrocnemii muscle of dogs. These results permitted more accurate calculations of the number of vesicles crossing the endothelium in one direction/sec/(μm² (～6·2), and of the median vesicular attachment time (～8 sec). The probability of fusion occurring when a vesicle contacts a plasma membrane (α= 0·004) was unchanged: hence it was concluded, from the mean cellular width (0·21 μm) and the calculated cytoplasmic viscosity (～0·1 poise), that ～49% of the vesicles starting from one side reached the other one, and that their median transit time was ～1 sec.