384 THE HUMAN BODY 



generally, to filter out organisms from the lymph stream, are 

 peculiarly liable to invasion by the organisms of common colds 

 and also by those which form pus (streptococcus). When any of 

 these become established in the tonsils and set up inflammation 

 therein the very painful condition called tonsilitis results. In 

 many cases the tonsils become permanently infected. In such 

 there is a steady production of toxins which are discharged into 

 the lymph stream and thence pervade the Body. Malnutrition 

 in children and adults is often to be accounted for solely on the 

 basis of chronic poisoning from infected tonsils. There is also 

 reason to believe that acute rheumatism is caused similarly. In 

 such cases the possible good that may come to the Body from the 

 normal functioning of the tonsils is so far outweighed by the harm 

 they do as seats of infection that they should obviously be removed. 

 The Movement of the Lymph. This is no doubt somewhat 

 irregular in the commencing vessels, but, on the whole, sets on 

 to the larger trunks and through them to the veins. In many 

 animals (as the frog) at points where the lymphatics communicate 

 with the veins, there are found regularly contractile "lymph- 

 hearts" which beat with a rhythm independent of that of the 

 blood-heart, and pump the lymph into a vein. In the Human 

 Body, however, there are no such hearts, and the flow of the 

 lymph is dependent on less definite arrangements. It seems to 

 be maintained mainly by three things: (1) The pressure on the 

 blood-plasma in the capillaries is greater than that in the great 

 veins of the neck; hence any plasma filtered through the capillary- 

 walls will be under a pressure which will tend to make it flow to 

 the venous termination of the thoracic or the right lymphatic 

 duct. (2) On account of the numerous valves in the lymphatic 

 vessels (which all only allow the lymph to flow past them to 

 larger trunks) any movement compressing a lymph-vessel will 

 cause an onward flow of its contents. The influence thus exerted 

 is very important. If a tube be put in a large lymphatic, say at 

 the top of the leg of an animal, it will be seen that the lymph only 

 flows out very slowly while the animal is quiet; but as soon as it 

 moves the leg the flow is greatly accelerated. (3) During each 

 inspiration the pressure on the thoracic duct is less than that in 

 the lymphatics in parts of the Body outside the thorax (see 

 Chap. XXIII). Accordingly, at that time, lymph is pressed, or, 



