3 oo PR OD 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 now 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 
now 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. 
Eespiration 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 tart 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 lie 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. Avery similar arrangement of lymphatics has been described 
bv 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. z% Leipzig, 1876. 
2 "Die Lymphgefasse der Fascien und Sehnen," Leipzig, 1872. 
3 Arb. a. d. physiol. Anst. :» Leipzig, 1866. 4 Ibid., 1S70. 
