CHAPTER XIV 

 LYMPH AND TISSUE FLUIDS 



IN no part of the body does the blood come in actual contact with the living 

 cells of the tissue. In all parts the blood flows in capillaries with definite 

 walls consisting of a single layer of cells, and is thus separated from the 

 tissue -elements by these walls and by a varying thickness of tissue. In some 

 organs, such as the liver and lung, every cell is in contact with the outer 

 surface of some capillary ; while in others, such as cartilage (which is quite 

 avascular), a considerable thickness of tissue may separate any given cell 

 from the nearest capillary. A middleman is thus needed between the blood 

 and the tissues, and this middleman is the tissue fluid or lymph which fills 

 spaces between all the tissue elements, so that any tissue can be regarded as 

 a sponge soaked with lymph. 



Throughout these spaces we find a close network of vessels, lined and 

 separated from the tissue spaces by a layer of extremely thin endothelial 

 cells, and this plexus communicates with definite channels lymphatics, 

 by which any excess of fluid in the part is drained off. The lymphatics 

 all run towards the chest, where those of the hind limbs join a large vessel 

 (the receptaculum chyli), which receives the lymph from the alimentary canal, 

 to form the thoracic duct. This runs up on the left side of the oesophagus, 

 and after receiving the lymphatic trunks from the left fore limb and the left 

 side of the neck, opens into the venous system at the junction of the left 

 internal jugular with the subclavian vein. A small vessel on the right side 

 drains the lymph from the right fore limb and right side of -the chest and 

 neck. 



The lymph may be looked upon as a part of the plasma which exudes 

 through the capillary wall, bathes all the tissue elements, passes between 

 the endothelial cells into the peripheral lymphatic network, whence it is 

 carried by lymphatic trunks into the thoracic duct, by which it is returned 

 again to the blood. 



It is easy to obtain lymph for examination by putting a cannula (a small 

 tube of glass or metal) into the thoracic duct, and collecting the fluid that 

 drops from it in a glass vessel. 



We may also tap in a similar way one of the large lymphatic trunks of the 

 limbs ; but in the latter case we have to use artificial means to induce a flow 

 of lymph, since little or none can be obtained from a limb at rest, the only 

 part of the body where there is normally a constant flow of lymph being the 



1061 



