FORMATION OF JA Wff'H 333 



crystalloids while still in the vessels do not attract the fluids from the 

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

 secretion. 



"Wliile admitting- that in pathological conditions (e. g., passive con- 

 j^estion) pressure and filtration may play an important part, Heiden- 

 haiu considered that an active secretion by the endothelial cells 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," Ileidenhain meaning by this term such 

 chemical and physical forces of living cells as are unliJiown 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, liave 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 tissues and organs, rather than to those 

 of the capillary 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 l)y which the cells, whether en- 

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

 Meltzer 1 has made an interesting suggestion, as follows: Considering the prop- 

 erty of endothelial cells to act as phagocytes, MacCallum " has shown tliat solid 

 granules (e. f/., coal pigment, carmin) are taken throujrh the walls of the lymphat- 

 ics by the phagocytic activity of their endothelial cells. ]\Ieltzer suggests tliat in 

 a similar way the endothelial cells may transport through the vessel-walls not 

 only solid particles, ])ut also, by the same mechanism, substances in solution; 

 and for this hypothetical process he suggests tlie name "potoci/tosis." 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 tlie process. Xo experimental evi- 

 dence 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. 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 



sAmer. Jour. Physiol.. IflOO (.3), p. xix: Zeit. f. Biol.. 1000 UO), 207. 



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



s Lancet, 1896 (i), Jlay 9, et seq.; Sch:i,fer's Text-book of Physiology, vol. 1. 



