532 TRANSUDATION. [BOOK n. 



divided, the flow of lymph from the foot on that side is greater than 

 on the intact side ; the section of the sciatic leads to the arteries 

 being dilated and the capillary pressure being increased. If the 

 peripheral end of the nerve be stimulated and the arteries in 

 consequence constricted (the complication of muscular movements 

 being avoided by the use of urari), the flow is diminished instead of 

 being increased; if however the stimulation be conducted ( 168) 

 so as to lead to dilation not constriction of the arteries, the flow is 

 still further increased. Again, stimulation of the lingual nerve on 

 one side, which leads to dilation of the arteries in the corresponding 

 side of the tongue, causes osdema of that half of the tongue ; the 

 lymph is transuded into the tissues more rapidly than it can be 

 carried away. So also when the cervical sympathetic in a rabbit 

 is divided there is an increased transudation in the ear. But we 

 need not appeal to such abnormal events as the above. When 

 impulses pass down the chorda-tympani nerve, they lead to a 

 widening of the arteries of the submaxillary gland, and the re- 

 sulting increased capillary pressure leads to an increased trans- 

 udation of lymph ; it is this increase of lymph which furnishes the 

 water (and other substances) of the saliva secreted ; and the 

 quantity of saliva secreted shews how great must be the quantity of 

 lymph transuded. The matter is here complicated by the cells of 

 the gland continually drawing upon the lymph, using it up for the 

 manufacture of the saliva instead of letting it flow away by the 

 lymph-channels, and thus tending to create, so to speak, a vacuum 

 of lymph outside the capillaries ; but this does not prevent the 

 case being one in which increased capillary pressure causes 

 increased transudation. And indeed we may say generally that 

 the dilation of arteries accompanying the activity of "an organ has 

 for one of its chief purposes an increase of transudation brought 

 about by the increased capillary pressure. 



But the increase of transudation due to increase of capillary 

 pressure is still more striking when that increase is due to events 

 taking place on the venous side of the capillaries. When a vein is 

 obstructed, as for instance by clot or by a ligature, oedema of the 

 parts from which the vein gathers its blood is a most common 

 result ; the lymph transudes so fast that it cannot be carried away 

 from the tissues with adequate rapidity. Again, in cases of heart 

 disease where there is an obstacle to the proper passage of the 

 blood through the heart, and the blood accumulates on the venous 

 side, leading to an increased venous pressure, and so to an increased 

 capillary pressure, oedema, especially of the lower limbs, is a 

 common result. And the fulness of the hand which has been for a 

 long time hung down, is probably due, not only to the flow of 

 lymph being checked but to the increased venous pressure in- 

 creasing the transudation. Again, when in a dog the flow from a 

 cannula in the thoracic duct is watched, this will be found to be 

 greatly increased if the inferior vena cava be obstructed above the 



