280 EDEMA 



one place to another, Meltzer 1 has made an interesting suggestion, as 

 follows : Considering the property of endothelial cells to act as phago- 

 cytes, MacCallum 2 has shown that solid granules (e. g., coal pigment, 

 carmin) are taken through the walls of the lymphatics by the phagocytic 

 activity of their endothelial cells. Meltzer suggests that in a similar 

 way the endothelial cells may transport through the vessel-walls not only 

 solid particles, but also, by the same mechanism, substances in solution ; 

 and for this hypothetical process he suggests the name ' ' potocytosis." 

 There can be little question that cells do take up substances in solution, 

 and sometimes this is done in an apparently selective manner ; e. g., the 

 taking up of bacterial toxins and vegetable poisons in the peritoneal 

 cavity by the leucocytes. Presumably the mechanism of "potocytosis" 

 is not different from that of phagocytosis, chemotactic forces determining 

 the occurrence of the process. No experimental evidence has been 

 advanced as yet for this very plausible hypothesis. 



Permeability of Capillaries. In explanation of the 

 variability in the amount and composition of the lymph, Star- 

 ling 3 has introduced the factor of altered permeability of the 

 capillary walls, which presumably depends upon the number 

 and size of the pores. He found that normally the lymph 

 coming from the lower extremities contains only 2 per cent, to 

 3 per cent, of proteids, while lymph from the intestines con- 

 tains 4 per cent, to 6 per cent., and lymph from the liver con- 

 tains 6 per cent, to 8 per cent, of proteids ; hence he considers 

 that the liver capillaries are the most permeable, i. e., have the 

 largest pores, so that more of the large colloid molecules can 

 escape from them. The effect of lymphagogues of the first 

 class (peptones, etc.) he attributes to their poisonous properties, 

 and the consequent injury to, and alterations in, the capillary 

 wall. The crystalloidal lymphagogues, he believes, act by first 

 attracting fluids from the tissues into the blood with a resulting 

 " hydremic plethora," which in turn leads to increased blood 

 pressure and consequent filtration of a watery fluid out of the 

 vessels. He considers, therefore, that the amount and quality 

 of the lymph produced in any part are determined solely by two 

 factors, the intracapillary blood pressure and the permeability 

 of the capillary walls. 



In connection with this question of the permeability of the 

 capillary walls, Meltzer suggests that the contractility and irri- 

 tability of the endothelium may be a potent factor in deter- 

 mining the size of the pores in the capillary walls. When in 

 a tonic condition, the endothelium is firmly contracted about 

 the pores, keeping their size small ; when the endothelial cells 



1 Loc. tit. 



2 Johns Hopkins Hosp. Bull., 1903 (14), 1. 



3 Lancet, 1896 (i), May 9, et seq.; Schiifer's Text-book of Physiology, vol. 1. 



