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 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, to open into the venous system at the junc- 

 tion of the left internal jugular with the subclavian vein. A small 

 vessel on the right side drains the lymph from the right upper 

 extremity 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 canhula 

 (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 



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