516 SOLITARY FOLLICLES. [BOOK n. 



A solitary follicle consists essentially of a spherical mass of 

 fine adenoid tissue the meshes of which are crowded with 

 leucocytes. In the intestine as we have seen ( 259) the con- 

 nective tissue lying between the epithelium above and the 

 muscularis mucosse below has a reticular arrangement and con- 

 tains leucocytes; but in the follicle the network is finer, closer 

 and more regular than elsewhere, the meshes are almost completely 

 filled with leucocytes, and the spherical mass breaking through the 

 muscularis mucosse reaches some way down into the submucous 

 tissue. Over the surface of the follicle, which bulges somewhat 

 into the interior of the intestine, villi may be present, but the 

 glands of Lieberkiihn are pushed aside and are found only at 

 its circumference. Into this mass of adenoid tissue one or more 

 small arteries enter and break up into a capillary network the 

 blood from which is carried away by one or more small veins. 

 Around the mass there is placed a more or less well developed 

 spherical lymph-space, lined with sinuous epithelioid plates and 

 continuous with the neighbouring lymphatic vessels. This lymph- 

 space or lymph-sinus as it is called thus forms a hollow jacket 

 filled with lymph round the spherical mass of adenoid tissue, but 

 is not complete, being broken by the entering and issuing blood 

 vessels, or by imperfect partitions passing from the tissue without 

 to the adenoid tissue within. The blood vessels and bridles in 

 question are covered by a layer of epithelioid plates continuous 

 with that lining the outer wall of the jacket, as also with the one 

 which more or less completely invests the inner mass of adenoid 

 tissue. 



The leucocytes which occupy the meshes are of different sizes. 

 Some are as large or almost as large as white blood-corpuscles ; 

 the majority however are much smaller than white blood-corpuscles, 

 their smallness being chiefly due to the small amount of cell- 

 substance surrounding the nucleus ; in some only a mere film of 

 cell-substance can be detected so that the nucleus appears almost 

 as a so-called ' free ' nucleus. Many of the leucocytes may be seen 

 to be undergoing nuclear changes, indicating that they are multi- 

 plying by mitotic division ; and indeed there are many reasons for 

 thinking that in the adenoid tissue of these follicles and other 

 similar structures a very considerable multiplication of leucocytes 

 takes place. Many of the leucocytes of these follicles exhibit under 

 favourable circumstances amreboid movements, and the smaller 

 leucocytes, indeed even the smallest, seem at times as active as 

 the larger ones. 



A solitary follicle then may be considered as consisting in the 

 first place of a rounded capillary network fed and drained by 

 small arteries and veins, all supported by a minimal amount of 

 ordinary connective tissue. In the second place the interstices 

 of this vascular network are filled up with adenoid tissue the fine 

 meshes of which are crowded with leucocytes of variable but on 



