PROPERTIES AND FORMATION OF LYMPH 243 



date, but in a more unmistakable manner in the latter. This result 

 proves very clearly that the capillary wall possesses a certain selective 

 power which enables it to keep the NaCl-content of the blood constant 

 by f acihtating the escape of the superfluous quantity of this salt. That 

 the lining cells are also capable of furthering the escape of water has 

 been demonstrated by the experiments of Carlson, Greer and Becht.^ 

 It seems that the lymph in the cervical ducts of the horse or dog may 

 acquire a molecular concentration much below that of the blood; 

 in fact, the difference may become so great at times that it cannot be 

 explained upon the basis of ordinary hydrostatic laws. The secretory- 

 properties of the capillary lining cells are also proved in an indirect 

 way by the fact that the cellular components of the salivary glands, 

 kidneys and pancreas completely dominate the quantity and quality 

 of their respective secretions. If this power is conceded to one group 

 of cells, it would be dilSicult to deny it to other groups of cells. An 

 impartial consideration of the evidence, therefore, must lead us to con- 

 clude that the formation of lymph is dependent upon (a) differences in 

 pressure between the blood and lymph spaces, (6) differences in the 

 concentration of the body fluids, and (c) true secretory properties on 

 the part of the cells forming the capillary walls. Thus, the three fac- 

 tors engaged in this process are: filtration, diffusion and osmosis and a 

 vital activity of the capillary ceils. 



The Factors Controlling the Flow of L3miph.— It has been stated 

 above that the lymph is formed among the cells of the different 

 tissues and that it moves from here with varying rapidity into the 

 larger collecting channels, whence it again reaches the vascular system. 

 The plasma thus temporarily diverted at the periphery into extra- 

 vascular spaces, is eventually returned to the blood traversing the cen- 

 tral circulatory system. A picture, the impressiveness of which 

 can scarcely be surpassed, is presented at the point of confluency 

 between the thoracic duct and the left subclavian vein. The clear 

 lymph intermingles here with the dark venous blood in the manner 

 of two rivers carrying varying amounts of sedimentous material. 

 This picture is especially fascinating about two hours after the inges- 

 tion of fatty food, i.e., after the lymph has assumed a milky appearance 

 in consequence of its high molecular content in fat. The entire duct 

 is then sharply outUned and may be followed to the receptaculmn 

 chyU and its tributary radicles upon the surfaces of the intestine. 

 The discussion pertaining to this subject may be arranged as follows: 



1. While the pressure under which the lymph is retained in the smallest chan- 

 nels amounts to only 10 to 15 mm. H2O, it nevertheless decreases steadily in the 

 direction from the tissues to the orifices of the main lymphatic ducts. Lymph is 

 formed peripherally under a capillary blood pressure which may be reckoned at 

 about 40 mm. Hg., while the pressure encountered in the central venous trunks 

 amounts to — 5 mm. Hg.2 Lymph, therefore, flows from a place of high pressure 

 to a place of low pressure, but the decline is not- equally rapid in all parts of the 



1 Am. Jour, of Physiol., xix, 1907, 360. 



2 Burton-Opitz, Am. Jour, of Physiol., ix, 1903, 198. 



