34 GENERAL STRUCTURE OF THE BODY. 



out and there being no circulation to bring it back. 

 This condition is called oedema and occurs in liver, 

 kidney, and heart troubles, being generally first ob- 

 served at the ankles. In ascites, hydrothorax, hydro- 

 cephalus, and pericardial and pleural effusions the fluid 

 corresponds to lymph in its composition and the large 

 amount is due to excessive formation of the fluid, which 

 is normally present in small quantities. 



Lymph gives the tissues substances from the blood 

 that they need and carries off those they do not, whether 

 waste or substances of use to other tissues. Because 

 they thus absorb certain materials not needed by the 

 tissues and convey them to the circulation, the lymph- 

 atics have also been called absorbents. Indeed, lymph 

 may be spoken of as the middleman between the blood 

 and the tissues. 



Another function of the lymph is to lubricate. Thus, 

 the synovial fluid of the joints is lymph and the pleurae 

 and the pericardium contain lymph or serum to reduce 

 the friction between the adjoining surfaces as much as 

 possible. The brain and spinal cord do not quite fill 

 the cavities of the cranium and the spinal column but 

 float on a cushion of lymph, the cerebro-spinal fluid. 

 When the brain, which is subject to increase and dimi- 

 nution in size, increases in size, it drives the lymph out, 

 and when it diminishes, the lymph returns. 



The lymph glands serve as a protection to adjacent 

 parts and when it leaves the gland the lymph is purer 

 and richer in leucocytes than when it entered. In fact, 

 they filter harmful matter from the lymph and appar- 

 ently also form white corpuscles. Normally they can 

 with difficulty be felt, but in disease, if the leucocytes 

 are unable to destroy or carry off the poison, the lymph 

 carries it along to the glands, which swell and become 

 tender. If the infection is not severe the swelling goes 

 down and the tenderness passes after a short time, but 

 if it is severe, there may be suppuration and abscess for- 

 mation and the gland even perhaps be' destroyed, giving 



