LYMPHATIC SYSTEM AND DUCTLESS GLANDS. 353 



riphery of the gland, and efferent vessels arise in its centre. 

 Hence the lymph in its flow traverses the cellular gland sub- 

 stance, and in its course picks up extra corpuscles which it 

 carries on to the blood. In the lymphoid tissue there is a 

 close network of blood-capillaries. It is clear that these 

 organs are not true glands, in the proper sense of the word: 

 they are sometimes called lymphatic ganglia, but that sug- 

 gests a connection with nerve-centres; a good name for them 

 is lymphatic nodes. In Fig. 12| is given a diagrammatic rep- 

 resentation of a lymphatic node. 



tr 



Fm. 121 Diagram of cross-section of a lymphatic gland : al, afferent lymphatic 

 vessels; el, efferent lymphatic vessel; tr. one of the connective-tissue bands sub- 

 dividing: the gland ; C, cortical portion: M. medullary portion. The leucocytes are 

 represented only in a part of the right half of the figure, where they are seen, Ih. 

 to lie closely packed in the centre of a gland-chamber, while towards the walls of 

 the chamber, 7.9, where they are naturally less closely packed, they have been 

 washed away, as often happens in preparing a specimen, leaving the reticular sup- 

 porting tissue conspicuous. 



The Movement of the Lymph. This is no doubt some- 

 what 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 con- 

 tractile "lymph-hearts" which beat with a rhythm independ- 

 ent of that of the blood-h'eart, 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 capil- 

 laries is greater than that in the great veins of the neck; 

 hence any plasma filtered through the capillary-walls will be 



