42 THE BODY AT WORK 



lymph escapes in undue quantity from the blood-stream, or 

 escapes more rapidly than it is absorbed ; the nutritive condi- 

 tion of the endothelium is disturbed. Its unusual permeability 

 is due in part, no doubt, to the dilatation of the capillary tube, 

 the stretching of its membranous wall ; but it is due also to 

 the diminished vigour of the endothelial cells. They have 

 lost to a certain extent their capacity for holding their edges 

 in perfect apposition. 



When the circulation is sluggish, owing to the inefficiency 

 of the heart, the tissues become cedematous. In other words, 

 lymph accumulates in the tissue-spaces. When the skin of a 

 healthy person is pressed, it returns to its natural position 

 as soon as the pressure is removed. If there is a tendency 

 to dropsy for ages the term " hydropsia " has been thus 

 familiarly clipped the finger leaves a pit behind it when 

 pressed upon the skin. It is some little time before the 

 lymph in the connective- tissue sponge readjusts the surface. 

 Excessive escape of lymph from the blood, or its insufficient 

 return into the blood, may also be the result of obstruction to 

 the flow in the great veins. When the veins of the leg are 

 varicose, the weight of the column of blood in the distended 

 vessels impedes its circulation. After standing, the tissues 

 about the ankle become cedematous. The oedema disappears 

 on lying down. A hardening (cirrhosis) of the liver impedes 

 the circulation of the blood which comes to it through the 

 portal vein from the walls of the alimentary canal. The 

 capillaries of the stomach and intestine are distended. Lymph 

 accumulates in the abdominal cavity, producing ascites, 

 another form of dropsy. 



It is almost hopeless to attempt to disentangle the various 

 factors which disturb the balance between blood and lymph 

 excessive outflow from blood, deficient inflow from lymph, 

 stretching of the endothelium of the capillary tubes, imperfect 

 nutrition and consequent imperfect apposition of the endo- 

 thelial scales, increased permeability of the scales. The 

 exudation which accompanies inflammation would seem to be 

 due to the diminished vitality of the endothelium rather than 

 to a mechanical factor, such as increased blood-pressure in 

 the capillaries, and their consequent distention. Ascites is, 

 apparently, a purely mechanical result of the resistance offered 



