LYMPH AND TISSUE FLUIDS 1141 



it in the thoracic cavity is materially aided by the respiratory move- 

 ments ; since, with every inspiration, the lacteals and abdominal part 

 of the duct are subjected to a positive pressure, and the intrathoracic 

 part of the duct to a negative pressure, so that lymph is continually 

 being sucked into the thorax. 



THE ABSORPTION OF LYMPH AND TISSUE FLUIDS 

 On injecting a coloured solution or suspension into the connective 

 tissues of any part of the body, and gently kneading the part, it is found 

 that the fluid fills all the lymphatic channels running from the part ; 

 and we can in this way inject the lymphatics of the limb and trace their 

 course on to the thoracic duct. The same path is taken by micro- 

 organisms as they spread in the tissues, or by particles of carmine 

 or Indian ink which have been introduced in tattooing. It is on account 

 of these facts that the lymphatics are often spoken of as the ' absorbent 

 system.' 



This process of lymphatic absorption is, however, a slow one, 

 unless aided to a large extent by passive or active movements of the 

 surrounding parts, and cannot therefore account for the rapid symp- 

 toms of poisoning which supervene within two or three minutes after 

 the hypodermic injection of a solution of strychnine or other poison. 

 That this absorption is not dependent on the lymphatics is shown 

 by the fact that the symptoms occur almost as quickly when all the 

 tissues of the limb have been severed with the exception of the main 

 artery and vein. In the same way, after injecting methylene blue or 

 indigo carmine into the pleural cavity or subcutaneous tissues, the 

 dyestuff appears in the urine long before any trace of colour can be 

 perceived in the lymph flowing from the thoracic duct. The absorption 

 in these cases is by the blood-vessels, and consists in an interchange 

 between blood and extra vascular fluids, apparently dependent entirely 

 upon processes of diffusion between these two fluids. So long as any 

 difference in composition exists between the intra- and extravascular 

 fluids, so long will diffusion-currents be set up, tending to equalise this 

 difference. 



More difficulty is presented by the question of the mechanism of 

 absorption by the blood-vessels of the normal tissue fluids such an 

 absorption as we have seen to occur after loss of blood by haemorrhage. 

 It seems probable that this absorption depends on the small 

 proportion of protein contained in the tissue fluid as compared with 

 the blood-plasma, and is due to the osmotic pressure of the 

 protein. If blood-serum be placed in a bell-shaped vessel (the 

 mouth of which is closed by a gelatinous membrane which does not 

 permit the passage of protein), and suspended in normal salt solution, 

 it is found that the serum absorbs the salt solution until the manometer 



