3 oo PROD UCTION AND ABSORPTION OF L YMPH. 



connective tissue, that a rise of tension in the meshes of the latter will 

 only drag the walls of the lymphatics further apart, and thus increase 

 rather than diminish their lumen. 1 



Although the blood pressure is therefore the primary mechanical 

 factor in the movement of lymph, there are several other factors which, 

 though subsidiary, are of considerable importance. In the first place, the 

 flow of lymph through the thoracic duct is much aided by the respira- 

 tory movements. In all experiments on the subject of lymph formation, 

 it is necessary to maintain the animal in as quiet a condition as possible, 

 since any disturbance of the respiratory movements causes a variation 

 in the lymph flow from the thoracic duct. With every inspiration, in 

 consequence of the descent of the diaphragm, there is a rise of pressure 

 in the abdominal cavity, and a fall of pressure in the thorax. Hence 

 we get an emptying of the lymphatics of the abdomen, including the 

 receptaculum chyli, and a distension of the duct in the thoracic 

 cavity. With each expiration the thoracic duct tends to collapse 

 to a certain degree and so empties itself into the veins, a backward 

 flow of lymph being prevented by the valves in the duct. If a 

 manometer be connected by a T-tube with the thoracic duct, it is 

 found that there is a rise of pressure during expiration and a fall 

 during inspiration, so that during the latter period the pressure may 

 become negative. 



Respiration has also an indirect influence on the lymph flow. With 

 each inspiration the negative pressure in the thorax is increased, so that 

 a negative pressure is also produced in the intrathoracic venous trunks, 

 which must cause a suction of lymph through the thoracic duct into the 

 subclavian vein. That the blood pressure in the subclavian vein at 

 the opening of the thoracic duct is of importance for the flow of lymph, 

 is shown by the fact that, if the pressure here is raised in any way, as by 

 ligature of the vein, the flow of lymph is entirely stopped, and there 

 may be a reflux of blood from the vein into the duct. 



The work of Ludwig and his pupils has revealed to us the existence 

 of certain anatomical arrangements for furthering the flow of lymph. 

 Thus, in all tendons and aponeuroses of the body, we find a double 

 system of lymphatics, consisting of a deep network of capillaries with 

 meshes elongated in the direction of the fibrous bundles, and lying 

 directly on the muscular fibres ; and a superficial network with polygonal 

 meshes lying in the peritendinous connective tissue. 2 Both networks 

 are in connection by means of small vertical branches, and contain no 

 valves. It is found that the slightest pressure or stretching of the 

 aponeuroses causes a flow of lymph from the deep into the superficial 

 meshwork, and from here into larger lymphatic vessels, which pass 

 through the substance of the muscles to join the large lymphatic 

 trunks. A very similar arrangement of lymphatics has been described 

 by Ludwig and Schweigger-Seidel, 3 in the central tendon of the 

 diaphragm. These may be injected by introducing some coloured fluid 

 into the abdominal cavity of a freshly-killed animal, and then carrying 

 out artificial respiratory movements. 



The physiological proof of these deductions from anatomical obser- 

 vations was furnished by Genersich, 4 who showed that the lymph flow 



1 Gaskell, Arb. a. d. physiol. Anst. zu Leipzig, 1876. 



2 "Die Lymphgefasse der Fascien und Selinen," Leipzig, 1872. 



3 Arb. a. d. physiol. Anst. zu Leipzig, 1866. 4 Ibid., 1870. 



