430 BLOOD AND LYMPH. 



ing to this observer, the lymph formed in the liver is normally more 

 concentrated than that of the rest of the body. The occlusion of 

 the vena cava causes a marked rise in the capillary pressure in the 

 liver, and most of the increased lymph-flow under these circum- 

 stances comes from the liver; hence the greater concentration. 

 The results of this experiment, therefore, do not antagonize the 

 filtration-and-diffusion theory. 



3. Heidenhain discovered that extracts of various substances, 

 which he designated as " lymphagogues of the first class," cause a 

 marked increase in the flow of lymph from the thoracic duct, the 

 lymph being more concentrated than normal, and the increased flow 

 continuing for a long period. Nevertheless, these substances cause 

 little, if any, increase in general arterial pressure; in fact, if injected 

 in sufficient quantity they produce usually a fall of arterial pressure. 

 The substances belonging to this class comprise such things as pep- 

 tone, egg-albumin, extracts of liver and intestine, and especially 

 extracts of the muscles of crabs, crayfish, mussels, and leeches. 

 Heidenhain supposed that these extracts contain an organic 

 substance which acts as a specific stimulus to the endothelial cells 

 of the capillaries and increases their secretory action. The results 

 of the action of these substances has been differently explained by 

 those who are unwilling to believe in the secretion theory. Starling * 

 finds experimentally that the increased flow of lymph in this case, as 

 after obstruction of the vena cava, comes mainly from the liver. 

 There is at the same time in the portal area an increased pressure 

 that may account in part for the greater flow of lymph; but, since 

 this effect upon the portal pressure lasts but a short time, while 

 the greater flow of lymph may continue for one or two hours, it is 

 obvious that this factor alone does not suffice to explain the result 

 of the injections. Starling suggests, therefore, that these extracts 

 act pathologically upon the blood capillaries, particularly those of 

 the liver, and render them more permeable, so that a greater 

 quantity of concentrated lymph flows through them. Starling's 

 explanation is supported by the experiments of Popoff .f According 

 to this observer, if the lymph is collected simultaneously from the 

 lower portion of the thoracic duct, which conveys the lymph from 

 the abdominal organs, and from the upper part, which contains the 

 lymph from the head, neck, etc., it is found that injection of 

 peptone increases the flow only from the abdominal organs. Popoff 

 finds also that the peptone causes a dilatation in the intestinal 

 circulation and a marked rise in the portal pressure. At the same 

 time there is some evidence of injury to the walls of the blood- 

 vessels from the occurrence of extravasations in the intestine. As 



* "Journal of Physiology," 17, 30, 1894. 



f "Centralblatt f. Physiologie," 9, No. 2, 1895. 



