L YMPII. 73 



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 circumstances comes from the liver, 

 hence the greater concentration. The results of this experiment, therefore, do 

 not antagonize the filtration-and-diff'usion theory. 



3. Heidenhein 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 1 finds experi- 

 mentally 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 injec- 

 tions. 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 filters 

 through them. Starling's explanation is supported by the experiments of 

 Popotf. 2 According to this observer, if the lymph is collected simulta- 

 neously 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 will be found that injection of peptone 

 increases the flow from only 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 far, therefore, as the action of the lymphagogues of the first 

 class is concerned, it maybe said that the advocates of the filtration-and-diffu- 

 sion theory have suggested a plausible explanation in accord with their theory. 

 The facts emphasized by Heidenhain with regard to this class of substances do 

 not compel us to assume a secretory function for the endothelial cells. 



4. Injection of certain crystalline substances, such as sugar, Xa('l,and 

 other neutral salts, causes a marked increase in the (low of lymph from the 

 thoracic duct. The lymph in these cases is more dilute than normal, and the 



1 Journal of Physiology, L89 I. vol. xvii. p. 30. ' t vrdralblatt fur Physiologic, L895, Bd. Lx. No. 2. 



