FORCES CONCERNED IN MO VEMENT OF L YMPH. 299 



THE PHYSICAL FORCES CONCERNED IN THE MOVEMENT OF LYMPH. 



We may now consider briefly the forces which bring about the flow 

 of the lymph and chyle from the origin of the lymphatics towards the 

 termination of the thoracic duct in the subclavian vein. 



In the living animal the lymphatics, like the blood vessels, are in a 

 condition of moderate distension. The lateral pressure in the lymphatic 

 duct of the neck was measured in 1849 by Ludwig and Noll. 1 In the 

 dog they found that this pressure varied from 8 to 18 mm. sodium car- 

 bonate solution. A little later, Weiss 2 measured the pressure in the 

 same vessel in the dog and horse. In the dog he found that it varied 

 from 5 to 20 mm., and in the horse from 10 to 20 mm. soda solution. 

 The latter observer also estimated the velocity of the lymph flow in the 

 cervical lymphatic by means of Volkmann's hsemodromometer. He 

 found that the average velocity was about 4 mm. in the second, a 

 velocity which is exceedingly small as compared with the velocity of 

 blood in arteries or veins of the same calibre, and is only a few times 

 greater than the velocity in the capillaries. Since there is a constant 

 flow of lymph from the periphery to the thoracic duct, it is evident that, 

 as we trace the lymphatics towards their radicles, the pressure of the 

 lymph must increase. This increased pressure in the peripheral parts 

 of the lymphatic system is shown by the fact, to which Eudbeck 3 first 

 called attention, that if a lymphatic be emptied by pressure, it always 

 fills from the periphery, and if a ligature be placed round it, the vessel 

 swells upon the peripheral, and shrinks on the central side of the 

 ligature. 



We see then that the first and chief factor in the onward flow 

 of lymph is the pressure under which this is formed in the radicles 

 of the lymphatics and in the tissue spaces. As the blood flows through 

 the capillaries at a given pressure, a certain proportion of its fluid con- 

 stituents filteis through the vessel wall, forming a transudation which 

 is still under a certain amount of pressure, and it is this remaining 

 pressure which causes the onward flow of the lymph. Hence the 

 ultimate cause of the lymph flow must be looked for in the energy of 

 the heart's contraction. 



When this hypothesis was first put forward by Ludwig and Noll (in 

 opposition to the suction theories mentioned previously), it was objected 

 to by Donders 4 on anatomical grounds. At that time it was thought 

 that the lymphatics formed a closed system of capillaries, ramifying in 

 the tissues ; and Donders pointed out that if the pressure in the tissue 

 juices were higher than that of the contents of the lymphatic capillaries, 

 the effect would be, not a flow from spaces into capillaries, but a collapse 

 of the latter with obliteration of their lumen. Further anatomical 

 investigations have shown us, however, that, in the first place, the 

 lymphatics are probably not a closed system of tubes, but are in com- 

 munication with the tissue spaces (Eecklinghausen, 5 Ludwig); and 

 secondly, that the walls of the lymphatics, at any rate in certain situa- 

 tions, are 'so connected by strands of elastic fibres with the surrounding 



1 Loc. cit. 



2 " Experimentelle Untersuch. ueber die Lymphstrom, " Diss., Dorpat, 1860 (quoted by 

 Gruenhagen, Bd. i. S. 282). 



3 LOG. cit. 4 Ztsclir.f. rat. Med., 1853, N. F., Bd. iv. S. 238. 

 5 Strieker's "Histology," Syd. Soc. Trans., 1869, vol. i. p. 297. 



