FORMATION OF LYMI'II 333 



the lymph-spaces into the blood, and so cause rather a lessened lymph 

 secretion. 



While admitting that in pathological conditions {e. g., passive con- 

 gestion) pressure and filtration 7najj play an important part, Heiden- 

 hain considered that an active secretion by the endothelial colls is the 

 chief factor in the normal formation of lymph. The means by which 

 the cells perform this function was unknown; it was considered as an 

 example of "vital activity," Heidenhain meaning by this term such 

 chemical and physical forces of living cells as are unknown or not 

 understood at the present time, rather than any metaphysical concep- 

 tion of living matter, such as many vitalists assume. 



Other observers, corroborating Heidenhain's results for the most 

 part, have modified, or amplified his theory. Asher and his collabo- 

 rators, for example, ascribe the work done in causing lymph forma- 

 tion to the cells of the various 'issues and organs, rather than to those 

 of the capillar}'- wall. The increased flow of lymph from the salivary 

 gland that occurs during its activity they consider due to the work 

 of the gland cells, and its function the removal of products of metab- 

 olism. The action of such a lymphagogue as peptone they ascribe to 

 its stimulation of cellular activity, particularly in the liver, where it 

 causes an increased formation of bile. Gies^ and Asher also ob- 

 served that after an injection of crystalloidal lymphagogues, such as 

 sugar, a prolonged flow of lymph occurred after the death of the 

 animal, proving completely that such lymphagogic action is inde- 

 pendent of blood pressure. 



Potocytosis. — In explanation of the process by which the cells, whether en- 

 dothelial or tissue-cells, pass fluids through themselves from one place to another, 

 Meltzer^ has made an interesting suggestion, as follows: Considering the prop- 

 erty of endothelial cells to act as phagocytes, MacCallum* has shown that solid 

 granules (e. g., coal pigment, carmin) are taken through the walls of the lymphat- 

 ics 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, chemo- 

 tactic forces determining the occurrence of the process. No experimental evi- 

 dence has been advanced as yet for this very plausible hypothesis. 



Permeability of Capillaries. — In explanation of the variabihty 

 in the amount and composition of the lymph. Starling^ has introduced 

 the factor of altered permeability of the capillary walls, which pre- 

 sumably depends upon the number and size of the pores. He found 

 that normally the lymph coming from the lower extremities contains 



7 Amer. Jour. Physiol., 1900 (3), p. xix; Zeit. f. Biol., 1900 (40), 207. 



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



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



