AND BLOOD PRESSURE 163 



can stand a much longer anaemia than the heart and viscera, and 

 connected tissue and epithelia still longer. After the obstruction of 

 arteries, beyond the possibility of an efficient current being set up 

 by way of anastomotic pathways, the capillary-venous area of the 

 part affected fills by the slow inflow from surrounding areas, the 

 plasma passes out owing to the altered osmotic conditions, and 

 the red corpuscles heap together. Such congestion is seen in the 

 tongue of the curarised frog after tying the artery on either side 

 of the under surface. If the root of the ear of a rabbit be confined 

 by a ligature for eight to ten hours, and the string be loosened, 

 the ear swells and becomes very red, and the tissue lymph and 

 white corpuscles increase in the tissue spaces. After ligation for 

 twenty-four hours, small haemorrhages occur, the permeability of 

 the capillaries being then seriously altered. 



The effect of back congestion has been studied in the frog's 

 tongue after tying the veins which on either side carry the blood 

 from the tongue to the larger veins in the floor of the mouth 

 (Cohnheim, Thoma). The congestion can be observed micro- 

 scopically as it spreads backwards. The veins and capillaries 

 widen in the tongue, but scarcely so in the web of the foot where the 

 surrounding tissue is inextensile. As the plasma escapes into the 

 tissue spaces, the capillaries and veins become choked with red 

 corpuscles. If a cannula is placed in the lymphatics on the outer 

 side of the leg of a dog, and a ligature is drawn round the thigh so 

 as to obstruct the veins, the lymph before scarcely moving 

 begins to flow, and the foot may swell, gradually becoming 

 cedematous. Division of the vaso-constrictor nerves increases the 

 effect. This is well seen on obstructing the veins of the root of the 

 rabbit's ear and dividing the cervical sympathetic nerve. 



If the veins of the dog's leg are entirely obstructed by injecting 

 plaster of Paris into the vein on the dorsum of the foot confining 

 the thigh by a ligature during the injection the leg next day is 

 become cylindrical with O3dema. The kidney swells after ligation 

 of the renal vein to double or treble the size, and bloody extra- 

 vasations appear in its substance. In the frog's tongue the red 

 cells may be seen escaping through bulgings which appear in the 

 capillaries and small veins, that is when the venous obstruction 

 is complete. In all these cases increased capillary pressure is not 

 the prime cause of the phenomena. They result from stagnation, 

 altered metabolism, and altered osmotic energy And surface energy 



